Golf ball

ABSTRACT

The present invention is directed to a solid, non-wound, golf ball comprising two or more core components, and a cover component. The core components comprise i) a small, inner, high density, spherical center component comprising a blend of powdered metal and a first matrix material comprising polybutadiene and polyisoprene; and, ii) an outer core layer disposed about the spherical center component, formed from a second matrix material selected from the group consisting of a thermoset material, a thermoplastic material, or combinations thereof. The golf ball may further comprise a second or additional outer core layer(s) that surround the first outer core layer. Preferably, the inner, high density, center component is produced without the use of a crosslinking agent or coagent, which is the reaction product of an unsaturated carboxylic acid or acids and an oxide or carbonate of a metal such as zinc. The cover may be single or multi-layered.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 09/394,829, filed on Sep. 13, 1999, now U.S. Pat.No. 6,277,034. That application is a continuation-in-part of U.S. patentapplication Ser. No. 08/870,585, filed Jun. 6, 1997 now abandoned, whichis a continuation of U.S. patent application Ser. No. 08/556,237, filedNov. 9, 1995, now abandoned, which is a continuation-in-part of U.S.patent application Ser. No. 08/070,510 filed Jun. 1, 1993, nowabandoned. This application is also a continuation-in-part applicationof U.S. patent application Ser. No. 08/840,392, filed Apr. 29, 1997, nowissued as U.S. Pat. No. 5,779,562, which is a continuation-in-part ofU.S. patent application Ser. No. 08/631,613, filed Apr. 10, 1996, nowU.S. Pat. No. 5,803,831, which in turn is a continuation-in-part of U.S.patent application Ser. No. 08/591,046, filed on Jan. 25, 1996, nowabandoned, and U.S. patent application Ser. No. 08/542,793, filed onOct. 13, 1995, now abandoned, which in turn is a continuation-in-part ofU.S. patent application Ser. No. 08/070,510, filed on Jun. 1, 1993, nowabandoned. This application also claims priority to U.S. ProvisionalApplication Ser. No. 60/171,701, filed Dec. 22, 1999.

FIELD OF THE INVENTION

The present invention relates to golf balls and specifically to theconstruction of solid, non-wound, golf balls for regulation play. Moreparticularly, the invention is directed to improved golf ballscomprising multiple core assemblies which have a comparatively small,high density, polymeric center, or nucleus, component. The small, heavycenter component in combination with the particular remaining core andcover components produces a golf ball having a smaller moment of inertiaabout its central axis. This results in a golf ball which exhibitsenhanced spin while maintaining or improving additional golf ballcharacteristics such as durability, resiliency and compression.

Furthermore, the small, heavy weight, polymeric center component of theinvention is preferably produced without the use of one or more peroxidecrosslinking, or co-crosslinking agents comprising a metal salt of anunsaturated fatty or carboxylic acid. These crosslinking agents orcoagents are the reaction product of an unsaturated carboxylic acid oracids and an oxide or carbonate of a metal such as zinc. Examples ofsuch crosslinking agents, which again are preferably not incorporatedinto the present inventions, or if so, only to a minimal amount, includezinc diacrylate and zinc dimethacrylate. Accordingly, the polymericcenters of the golf balls of the present invention are generally freefrom peroxide crosslinking agents and exhibit high densities.

Additionally, in a more preferred aspect, the small, heavy centercomponent of the invention is produced through the use of a blend ofpolybutadiene and polyisoprene rubbers. Powdered metal materials andother materials, including curing agents, may be incorporated therein toproduce a high density, spherical center component that is commerciallyprocessible.

Moreover, in a particularly preferred aspect, the balls of the inventionfurther utilize a multi-layer cover assembly. The improved multi-layercover golf balls provide enhanced distance and durability propertiesover single layer cover golf balls while at the same time offeringenhanced “feel” and spin characteristics generally associated with softbalata and balata-like covers of the prior art.

BACKGROUND OF THE INVENTION

Golf balls traditionally have been categorized in three differentgroups, namely, as one piece balls, multi-piece solid (two or morepieces) balls, and wound (three piece) balls. The one piece balltypically is formed from a solid mass of moldable material which hasbeen cured to develop the necessary degree of hardness. It possesses nosignificant difference in composition between the interior and exteriorof the ball. These balls do not have an enclosing cover. One piece ballsare described, for example, in U.S. Pat. Nos. 3,313,545; 3,373,123; and,3,384,612.

The wound ball is frequently referred to as a three piece ball since itis made with a vulcanized rubber thread wound under tension around asolid or semisolid center to form a wound core and thereafter enclosedin a single or multilayer covering of tough protective material. Formany years the wound ball satisfied the standards of the U.S.G.A. andwas desired by many skilled, low handicap golfers.

The three piece wound ball typically has a balata cover which isrelatively soft and flexible. Upon impact, it compresses against thesurface of the club producing high spin. Consequently, the soft andflexible balata covers along with the wound cores provide an experiencedgolfer with the ability to apply a spin to control the ball in flight inorder to produce a draw or a fade or a backspin which causes the ball to“bite” or stop abruptly on contact with the green. Moreover, the balatacover produces a soft “feel” to the low handicap player. Suchplayability properties of workability, feel, etc. are particularlyimportant in short iron play with low swing speeds and are exploitedsignificantly by high skilled players.

However, a three piece wound ball also has several disadvantages. Forexample, a wound ball is relatively difficult to manufacture due to thenumber of production steps required and the careful control which mustbe exercised in each stage of manufacture to achieve suitable roundness,velocity, rebound, “click”, “feel”, and the like.

Additionally, a soft wound (three piece) ball is not well suited for useby the less skilled and/or high handicap golfer who cannot intentionallycontrol the spin of the ball. For example, the unintentional applicationof side spin by a less skilled golfer produces hooking or slicing. Theside spin reduces the golfer's control over the ball as well as reducingtravel distance.

Similarly, despite all the benefits of balata, balata covered balls areeasily cut and/or damaged if mishit. Consequently, golf balls producedwith balata or balata containing cover compositions, can exhibit arelatively short life spans. As a result of this negative property,balata and its synthetic substitute, trans-polyisoprene, and resinblends, have been essentially replaced as the cover materials of choiceby golf ball manufacturers by materials comprising ionomeric resins andother elastomers such as polyurethanes.

Conventional multi-piece solid golf balls, on the other hand, include asolid resilient core having single or multiple cover layers employingdifferent types of material molded on the core. The one piece golf balland the solid core for a multi-piece solid (nonwound) ball frequentlyare formed from a combination of materials such as polybutadiene andother rubbers cross linked with zinc diacrylate or zinc dimethacrylate,and containing fillers and curing agents which are molded under highpressure and temperature to provide a ball of suitable hardness andresilience. For multi-piece nonwound golf balls, the cover typicallycontains a substantial quantity of ionomeric resins that imparttoughness and cut resistance to the covers.

Ionomeric resins are generally ionic copolymers of an olefin, such asethylene, and a metal salt of a unsaturated carboxylic acid, such asacrylic acid, methacrylic acid or maleic acid. Metal ions, such assodium or zinc, are used to neutralize some portion of the acidic groupin the copolymer, resulting in a thermoplastic elastomer exhibitingenhanced properties, such as durability, for golf ball coverconstruction. However, some of the advantages gained in increaseddurability have been offset to some degree by decreases in playability.This is because, although the ionomeric resins are very durable, theyalso tend to be quite hard when utilized for golf ball coverconstruction and thus lack the degree of softness required to impart thespin necessary to control the ball in flight. Since most ionomericresins are harder than balata, the ionomeric resin covers do notcompress as much against the face of the club upon impact, therebyproducing less spin. In addition, the harder and more durable ionicresins lack the “feel” characteristic associated with the softer balatarelated covers.

As a result, while there are currently more than fifty (50) commercialgrades of ionomers available, both from DuPont and Exxon, with a widerange of properties which vary according to the type and amount of metalions, molecular weight, composition of the base resin (i.e. relativecontent of ethylene and methacrylic and/or acrylic acid groups) andadditive ingredients, such as reinforcement agents, etc., a great dealof research continues in order to develop golf ball cover compositionsexhibiting not only the improved impact resistance and carrying distanceproperties produced by the “hard” ionomeric resins, but also theplayability (i.e. “spin”, “feel”, etc.) characteristics previouslyassociated with the “soft” balata covers, properties which are stilldesired by the more skilled golfer.

Moreover, a number of multi-piece solid balls have also been produced toaddress the various needs of the golfing populations. The differenttypes of material used to formulate the core(s), cover(s), etc. of theseballs dramatically alter the balls' overall characteristics.

In this regard, various structures have been suggested using multilayercores and single layer covers wherein the core layers have differentphysical characteristics. For example, U.S. Pat. Nos. 4,714,253;4,863,167 and 5,184,828 relate to three piece solid golf balls havingimproved rebound characteristics in order to increase flight distance.The '253 patent is directed towards differences in the hardness of thelayers. The '167 patent relates to a golf ball having a center portionand an outer layer having a high specific gravity. Preferably, the outerlayer is harder than the center portion. The '828 patent suggests thatthe maximum hardness must be located at the interface between the coreand the mantle, and the hardness must then decrease both inwardly andoutwardly.

Similarly, a number of patents for multi-piece solid balls suggestimproving the spin and feel by manipulating the core construction. Forexample, U.S. Pat. No. 4,625,964 relates to a solid golf ball having acore diameter not more than 32 mm, and an outer layer having a specificgravity lower than that of the core. In U.S. Pat. No. 4,650,193, it issuggested that a curable core elastomer be treated with a cure alteringagent to soften an outer layer of the core. U.S. Pat. No. 5,002,281 isdirected towards a three piece solid golf ball which has an inner corehaving a gravity greater than 1.0, but less than or equal to that of theouter shell which must be less than 1.3. U.S. Pat. Nos. 4,848,707 and5,072,944 disclose three-piece solid golf balls having center and outerlayers of different hardness. Other examples of such dual layer corescan be found in, but are not limited to, the followings patents: U.S.Pat. Nos. 4,781,383; 4,858,924; 5,002,281; 5,048,838; 5,104,126;5,273,286; 5,482,285 and 5,490,674. It is believed that all of thesepatents are directed to balls with single cover layers.

Multilayer covers containing one or more ionomeric resins have also beenformulated in an attempt to produce a golf ball having the overalldistance, playability and durability characteristics desired. This wasaddressed in U.S. Pat. No. 4,431,193, where a multilayered golf ballcover is described as having been produced by initially molding a firstcover layer on a spherical core and then adding a second cover layer.The first or inner layer is comprised of a hard, high flexural modulusresinous material to provide a gain in coefficient of restitution whilethe outer layer is a comparatively soft, low flexural modulus resinousmaterial to provide spin and control. The increase in the coefficient ofrestitution provides a ball which serves to attain or approach themaximum initial velocity limit of 255 feet per second, as provided bythe United States Golf Association (U.S.G.A.) rules. The relativelysoft, low flexural modulus outer layer provides for an advantageous“feel” and playing characteristics of a balata covered golf ball.

In various attempts to produce a durable, high spin ionomeric golf ball,the golfing industry has also blended the hard ionomer resins with anumber of softer ionomer resins. U.S. Pat. Nos. 4,884,814 and 5,120,791are directed to cover compositions containing blends of hard and softionomeric resins. The hard copolymers typically are made from an olefinand an unsaturated carboxylic acid. The soft copolymers are generallymade from an olefin, an unsaturated carboxylic acid and an acrylateester. It has been found that golf ball covers formed from hard-softionomer blends tend to become scuffed more readily than covers made ofhard ionomer alone.

Most professional golfers and good amateur golfers desire a golf ballthat provides good distance when hit off a driver, control and stoppingability on full iron shots, and high spin for short “touch and feel”shots. Many conventional two piece and thread wound performance golfballs have undesirable high spin rates on full shots. The excessive spinon full shots is a sacrifice made in order to achieve more spin on theshorter touch shots. Consequently, it would be desirable to produce amulti-piece golf ball that exhibited low spin on full iron and woodshots and high spin in the “touch” and “feel” shots which occur with thehigh lofted irons and wedges around the green.

In this regard, the multi-piece nonwound balls, while having anadvantage with respect to cut resistance, typically have a cover that issufficiently hard so as to provide low deformation upon impact and asmall contact area between the ball and the club face. This provides agreater degree of “slipperiness” on the club face and, therefore, lesscontrol over the ball and greater difficulty in stopping the ball on thegreen when using short irons. At least some of these deficiencies areconsidered to result also from a large moment of inertia exhibited bythe multi-piece balls. Thus, it would be useful to develop a ball with acontrolled moment of inertia coupled with a soft cover layer in order toprovide the desired backspin when using short irons, but at the sametime without adversely impacting the desired flight and roll distance ofthe ball when using a driver.

A dual core, dual cover ball is described in U.S. Pat. No. 4,919,434.However, the patent emphasizes the hardness characteristics of alllayers, particularly the requirement for a soft inner cover layer and ahard outer cover layer. With respect to the core, it requires that thelayers should not differ in hardness by more than 10 percent and shouldbe elastomeric materials having a specific deformation range under aconstant load.

U.S. Pat. No. 5,104,126 attempts to concentrate the weight of the golfball in the center core region by utilizing a metal ball as the corecomponent. However, that patent teaches the use of a solid metal ball asthe core component which provides substantially different propertiesthan a polymeric core. Moreover, that patent also teaches the use ofdensity reducing filler materials incorporated elsewhere in the golfball. Although perhaps satisfactory in some respects, in other respects,it is undesirable to add density reducing fillers to offset the weightof the center core component. Additionally, it would be desirable tosimply avoid the use of density reducing fillers if possible as theytend to lower the resilience of the golf ball.

Moreover, golf balls utilized in tournament or competitive play todayare regulated for consistency purposes by the United States GolfAssociation (U.S.G.A.). In this regard, there are five (5) U.S.G.A.specifications which golf balls must meet under controlled conditions.These are size, weight, velocity, driver distance and symmetry.

Under the U.S.G.A. specifications, a golf ball can not weigh more than1.62 ounces (with no lower limit) and must measure at least 1.68 inchesin diameter (with no upper limit). However, as a result of the opennessof the upper or lower parameters in size and weight, a variety of golfballs can be made. For example, golf balls are manufactured today by theApplicants which are slightly larger (i.e., approximately 1.72 inches indiameter) while meeting the weight, velocity, distance and symmetryspecifications set by the U.S.G.A.

Additionally, according to the U.S.G.A., the initial velocity of theball must not exceed 250 ft/sec. with a 2% maximum tolerance (i.e., 255ft/sec.) when struck at a set club head speed on a U.S.G.A. machine.Furthermore, the overall distance of the ball must not exceed 280 yardswith a 6% tolerance (296.8 yards) when hit with a U.S.G.A. specifieddriver at 160 ft/sec. (clubhead speed) at a 10 degree launch angle astested by the U.S.G.A. Lastly, the ball must pass the U.S.G.A.administered symmetry test, i.e., fly consistency (in distance,trajectory and time of flight) regardless of how the ball is placed onthe tee.

While the U.S.G.A. regulates five (5) specifications for the purposes ofmaintaining golf ball consistency, alternative characteristics (i.e.,spin, feel, durability, distance, sound, visibility, etc.) of the ballare constantly being improved upon by golf ball manufacturers. This isaccomplished by altering the type of materials utilized and/or improvingconstruction of the balls. For example, the proper choice of thematerials for the cover(s) and core(s) are important in achievingcertain distance, durability and playability properties. Other importantfactors controlling golf ball performance include, but are not limitedto, cover thickness and hardness, core stiffness (typically measured ascompression), ball size and surface configuration.

Accordingly, a wide variety of golf balls have been designed and areavailable to suit an individual player's game. In essence, differenttypes of balls have been specifically designed or “tailor made” for highhandicap versus low handicap golfers, men versus women, seniors versusjuniors, etc. Moreover, improved golf balls are continually beingproduced by golf ball manufacturers with technological advancements inmaterials and manufacturing processes.

Two of the principal properties involved in a golf ball's performanceare resilience and compression. Resilience is generally defined as theability of a strained body, by virtue of high yield strength and lowelastic modulus, to recover its size and form following deformation.Simply stated, resilience is a measure of energy retained to the energylost when the ball is impacted with the club.

In the field of golf ball production, resilience is determined by thecoefficient of restitution (C.O.R.), the constant “e” which is the ratioof the relative velocity of an elastic sphere after direct impact tothat before impact. As a result, the coefficient of restitution (“e”)can vary from 0 to 1, with 1 being equivalent to a perfectly orcompletely elastic collision and 0 being equivalent to a perfectly orcompletely inelastic collision.

Resilience (C.O.R.), along with additional factors such as club headspeed, club head mass, angle of trajectory, ball size, density,composition and surface configuration (i.e., dimple pattern and area ofcoverage) as well as environmental conditions (i.e., temperature,moisture, atmospheric pressure, wind, etc.) generally determine thedistance a golf ball will travel when hit. Along this line, the distancea golf ball will travel under controlled environmental conditions is afunction of the speed and mass of the club and the size, density,composition and resilience (C.O.R.) of the ball and other factors. Thevelocity of the club, the mass of the club and the angle of the ball'sdeparture are essentially provided by the golfer upon striking. Sinceclub head, club head mass, the angle of trajectory and environmentalconditions are not determinants controllable by golf ball producers andthe ball size and weight are set by the U.S.G.A., these are not factorsof principal concern among golf ball manufacturers. The factors ordeterminants of interest with respect to improved distance are generallythe coefficient of restitution (C.O.R.), spin and the surfaceconfiguration (dimple pattern, ratio of land area to dimple area, etc.)of the ball.

The coefficient of restitution (C.O.R.) in solid core balls (i.e.,molded cores and covers) is a function of the composition of the moldedcore and of the cover. The molded core and/or cover may be comprised ofone or more layers such as in multi-layered balls.

In balls containing a wound core (i.e., balls comprising a liquid orsolid center, elastic windings, and a cover), the coefficient ofrestitution is a function of not only the composition of the center andcover, but also the composition and tension of the elastomeric windings.As in the solid core balls, center and cover of a wound core ball mayalso consist of one or more layers.

The coefficient of restitution of a golf ball can be analyzed bydetermining the ratio of the outgoing velocity to the incoming velocity.In the examples of this writing, the coefficient of restitution of agolf ball was measured by propelling a ball horizontally at a speed of125+/−1 feet per second (fps) against a generally vertical, hard, flatsteel plate and measuring the ball's incoming and outgoing velocityelectronically. Speeds were measured with a pair of Oehler Mark 55ballistic screens (available from Oehler Research Austin Tex.), whichprovide a timing pulse when an object passes through them. The screensare separated by 36″ and are located 25.25″ and 61.25″ from the reboundwall. The ball speed was measured by timing the pulses from screen 1 toscreen 2 on the way into the rebound wall (as the average speed of theball over 36″), and then the exit speed was timed from screen 2 toscreen 1 over the same distance. The rebound wall was tilted 2 degreesfrom a vertical plane to allow the ball to rebound slightly downward inorder to miss the edge of the cannon that fired it.

As indicated above, the incoming speed should be 125+/−1 fps.Furthermore, the correlation between C.O.R. and forward or incomingspeed has been studied and a correction has been made over the +/− fpsrange so that the C.O.R. is reported as if the ball had an incomingspeed of exactly 125.0 fps.

The coefficient of restitution must be carefully controlled in allcommercial golf balls if the ball is to be within the specificationsregulated by the U.S.G.A. As discussed to some degree above, theU.S.G.A. standards indicate that a “regulation” ball cannot have aninitial velocity exceeding 255 feet per second in an atmosphere of 75°F. when tested on a U.S.G.A. machine. Since the coefficient ofrestitution of a ball is related to the ball's initial velocity, it ishighly desirable to produce a ball having sufficiently high coefficientof restitution (C.O.R.) to closely approach the U.S.G.A. limit oninitial velocity, while having an ample amount of softness (i.e.,hardness) to produce the desired degree of playability (i.e., spin,etc.).

Furthermore, as mentioned above, the maximum distance a golf ball cantravel (carry and roll) when tested on a U.S.G.A. driving machine set ata club head speed of 160 feet/second is 296.8 yards. While golf ballmanufacturers design golf balls which closely approach this driverdistance specification, there is no upper limit for how far anindividual player can drive a ball. Thus, while golf ball manufacturersproduced balls having certain resilience characteristics in order toapproach the maximum distance parameter set by the U.S.G.A. undercontrolled conditions, the overall distance produced by a ball in actualplay will vary depending on the specific abilities of the individualgolfer.

The surface configuration of a ball is also an important variable inaffecting a ball's travel distance. The size and shape of the ball'sdimples, as well as the overall dimple pattern and ratio of land area todimpled area are important with respect to the ball's overall carryingdistance. In this regard, the dimples provide the lift and decrease thedrag for sustaining the ball's initial velocity in flight as long aspossible. This is done by displacing the air (i.e., displacing the airresistance produced by the ball from the front of the ball to the rear)in a uniform manner. Moreover, the shape, size, depth and pattern of thedimple affect the ability to sustain a ball's initial velocity.

As indicated above, compression is another property involved in theoverall performance of a golf ball. The compression of a ball willinfluence the sound or “click” produced when the ball is properly hit.Similarly, compression can effect the “feel” of the ball (i.e., hard orsoft responsive feel), particularly in chipping and putting.

Moreover, while compression of itself has little bearing on the distanceperformance of a ball, compression can affect the playability of theball on striking. The degree of compression of a ball against the clubface and the softness of the cover strongly influences the resultantspin rate. Typically, a softer cover will produce a higher spin ratethan a harder cover. Additionally, a harder core will produce a higherspin rate than a softer core. This is because at impact a hard coreserves to compress the cover of the ball against the face of the club toa much greater degree than a soft core thereby resulting in more “grab”of the ball on the clubface and subsequent higher spin rates. In effectthe cover is squeezed between the relatively incompressible core andclubhead. When a softer core is used, the cover is under much lesscompressive stress than when a harder core is used and therefore doesnot contact the clubface as intimately. This results in lower spinrates.

The term “compression” utilized in the golf ball trade generally definesthe overall deflection that a golf ball undergoes when subjected to acompressive load. For example, PGA compression indicates the amount ofchange in golf ball's shape upon striking.

The development of solid core technology in two-piece balls has allowedfor much more precise control of compression in comparison to threadwound three-piece balls. This is because in the manufacture of solidcore balls, the amount of deflection or deformation is preciselycontrolled by the chemical formula used in making the cores. Thisdiffers from wound three-piece balls wherein compression is controlledin part by the winding process of the elastic thread. Thus, two-pieceand multilayer solid core balls exhibit much more consistent compressionreadings than balls having wound cores such as the thread woundthree-piece balls.

Additionally, cover hardness and thickness are important in producingthe distance, playability and durability properties of a golf ball. Asmentioned above, cover hardness directly affects the resilience and thusdistance characteristics of a ball. All things being equal, hardercovers produce higher resilience. This is because soft materials detractfrom resilience by absorbing some of the impact energy as the materialis compressed on striking.

However, soft covered balls are generally preferred by the more skilledgolfer because he or she can impact high spin rates that give him or herbetter control or workability of the ball. Spin rate is an importantgolf ball characteristic for both the skilled and unskilled golfer. Asmentioned, high spin rates allow for the more skilled golfer, such asPGA and LPGA professionals and low handicap players, to maximize controlof the golf ball. This is particularly beneficial to the more skilledgolfer when hitting an approach shot to a green. The ability tointentionally produce “back spin”, thereby stopping the ball quickly onthe green, and/or “side spin” to draw or fade the ball, substantiallyimproves the golfer's control over the ball. Thus, the more skilledgolfer generally prefers a golf ball exhibiting high spin rateproperties.

In view in part of the above information, a number of one-piece,two-piece (a solid resilient center or core with a molded cover),three-piece wound (a liquid or solid center, elastomeric winding aboutthe center, and a molded cover), and multi-layer solid or wound golfballs have been produced to address the various needs of golfersexhibiting different skill levels. The different types of materialsutilized to formulate the core(s), cover(s), etc. of these ballsdramatically alter the balls' overall characteristics.

It would be useful to develop a golf ball exhibiting a high spin rate atlow club head speeds when using short, high lofted irons. Such a ballwould exhibit not only high spin but would also have a combination ofsoftness and durability which is better than the softness-durabilitycombination of a golf ball cover made from a hard-soft ionomer blend.Furthermore, it would be beneficial to produce a high spin golf ballthat produces enhanced spin characteristics independent of its specificcover composition alone.

These and other objects and features of the invention will be apparentfrom the following summary and description of the invention, thedrawings and from the claims.

SUMMARY OF THE INVENTION

Accordingly, it is a feature of the present invention to provide amulti-piece, nonwound, solid golf ball. The core is of a multilayerconstruction consisting of two or more polymeric components. Thecharacteristics of the polymeric components of the core are such thatthe moment of inertia may be adjusted to enhance the backspin of theball when using short irons.

An additional feature of the invention is to provide a ball having amultilayer polymeric core enclosed by a multi-layer cover. The ball hasan appropriate moment of inertia that will permit extended flightdistance of the ball and good roll when using a driver, coupled with acover having sufficient softness that will permit deformation of theball upon impact, thereby increasing the contact area between the balland the club face without subjecting the cover to undesirable cutting orabrasion.

Another feature of the present invention is the provision for a golfball of the type described that comprises both multilayer cores andcover(s) in such a manner as to incorporate the desirable featuresassociated with various categories of balls traditionally employed.

A further feature of the present invention is the provision for a golfball core structure with an inner or center polymeric core and an outerpolymeric core layer, with the inner core having a specific gravity thatdiffers from that of the outer core layer by more than 2.0, preferablymore than 3.0, and most preferably more than 6.0, thereby giving thegolf ball a moment of inertia differing from that of typical solid coreballs.

Yet another feature is the provision for a multilayer core that iscombined with a multilayer cover wherein the outer cover layer has alower hardness value than the inner cover layer.

A still further feature of the invention is the provision for a golfball having a soft outer cover layer with good scuff resistance and cutresistance coupled with relatively high spin rates at low club headspeeds.

The present invention provides in an additional aspect, a solid,nonwound golf ball, and comprising a multi-core assembly that isconcentrically positioned within the center of the golf ball, and amulti-layer cover assembly disposed about the multi-core assembly. Themass and position of both the multi-core assembly and the multi-layercover assembly are such that the moment of inertia of the golf ball isless than 0.45 oz. in², preferably less than 0.44 oz. in², and morepreferably, less than 0.43 oz. in² for a 1.680″ golf ball.

In yet another aspect, the present invention provides a golf ballcomprising a center core component which is concentrically disposedabout a reference point located at the geometric center of the golfball. The golf ball further comprises an outer core layer whichgenerally surrounds and is disposed about the center core component. Thegolf ball further comprises a first inner cover layer disposed andpositioned around the outer core layer, and a second outermost dimpledcover layer that is disposed about the first inner cover layer.Preferably, an ionomeric material is used in at least one of the coverlayers. The configuration of the golf ball is such that it has a momentof inertia is preferably less than 0.43 oz. in² for a 1.680″ golf ball.

In yet another aspect, the present invention provides a golf ballcomprising a center polymeric core component having a specific gravityin the range of from about 1.2 to about 20, preferably about 2.0 toabout 18.0, and a diameter in the range from about 5 mm to about 21 mm,preferably less than 10 mm. The golf ball further comprises an outercore polymeric layer disposed about the center core layer component, theouter core layer having a specific gravity in the range from about 0.9to about 1.2, and an outer diameter in the range from about 30 mm toabout 40 mm. The golf ball further includes an inner cover layerdisposed about the core layer, and an outer cover layer disposed aboutthe inner cover layer. The golf ball more preferably exhibits a momentof inertia of less than 0.43 oz. in², and a coefficient of restitutionof at least 0.760, preferably at least 0.780, and most preferably atleast 0.800.

In a still further aspect, the present invention relates to a multiplecore component, non-wound, golf ball having small, high density,spherical center which overcomes the above-referenced problems andothers. In this regard, a smaller (i.e., a diameter of from about 5 mm.to about 21 mm) and heavier spherical center or center core layer isproduced using a blend composed of a first polymer matrix materialcomprising a mix of polybutadiene and polyisoprene rubbers and metalparticles, or other high specific gravity filler materials. The blend ispreferably devoid of any metal carboxylate cross-linking orco-crosslinking agents generally present in solid core golf ballproduction.

In this respect, the high density center is encapsulated by one or moreouter core layers and a cover assembly comprising one or more layers.The outer core layer(s) comprise a second polymer matrix material. Thesize and weight of the outer core layer(s) comprising a second polymericmatrix material and/or cover layers are adjusted in order to produce anoverall golf ball which meets, or is less than, the 1.62 ounce maximumweight limitation specified by the U.S.G.A.

It has been found that the combination of the present invention producesa golf ball with a decreased moment of inertia and/or a lower radius ofgyration. This results in the generation of higher spin withoutsubstantially affecting the resiliency of the ball. Additionally, thegolf ball of the present invention exhibits a substantially similar orenhanced feel (i.e., softer compression) and overall durability.

In an additional aspect, the claimed subject matter of the presentinvention provides a golf ball comprising a dual polymeric core and acover. The dual core has an inner, high density, spherical center corelayer and at least one outer core layer. The high density, sphericalcenter comprises a blend of high density powdered metal and/or otherheavy weight filler materials and a first polymer matrix materialselected from thermosets, thermoplastics, and combinations thereof.Preferably, the first polymer matrix material comprises a blend of about90 to about 10 weight percent polybutadiene and of about 10 to about 90weight percent polyisoprene. More preferably, the first polymer matrixmaterial comprises of a blend of about 70 to about 30 weight percentpolybutadiene and from about 30 to about 70 weight percent polyisoprene.

Moreover, in this aspect, the inner, high density, center core layer ispreferably produced without the use of metal carboxylic crosslinkingagents that are generally utilized in solid golf ball core production.These crosslinking agents are the reaction product of an unsaturatedcarboxylic acid or fatty acids and an oxide or carbonate of a metal suchas zinc. Included are metal salts of unsaturated fatty acids, forexample zinc, aluminum, and calcium salts of unsaturated fatty acidshaving 3 to 8 carbon atoms, such as acrylic acid and methacrylic acid.

The size and weight of the center of this aspect is configured in amanner to produce a low moment of inertia and a reduced rate ofgyration. For example, the inner spherical center core layer has aspecific gravity of greater than 1.2, preferably greater than 4.0, andmost preferably greater than 7.0.

A lower density outer core layer is disposed about the high densityspherical center core layer. The outer core layer comprises a secondpolymer matrix material selected from thermosets, thermoplastics, andcombinations thereof. The second and first polymer matrix materials canbe of the same or different compositions. A cover is then molded aboutthe dual core.

In a still additional aspect, the present invention is directed to animproved dual core golf ball having a relatively small, high densityspherical center or nucleus containing powdered tungsten (or other highdensity powdered metals) in a first elastomeric matrix, such as a blendof polybutadiene and polyisoprene. The powdered metal elastomeric matrixis peroxide, sulfur or radiation crosslinked. Preferably no zincdiacrylate (ZDA), zinc dimethyl acrylate (ZDMA) or other unsaturatedcarboxylic cross-linking agents are included in the inner sphericalcenter.

One or more outer core layers are disposed about the high densitycenter, followed by one or more cover layers. The outer core and/orcover layers are made lighter and/or thicker in order to produce anoverall golf ball which conforms with the weight and size requirementsof the U.S.G.A. This combination of weight and size displacementdecreases the moment of inertia and/or allows the radius of gyration ofthe ball to move closer to the center.

The solid, non-wound, golf balls of the invention will have a moment ofinertia of less than 0.45 oz.in², preferably less than 0.44 oz.in² for astandard size golf ball. More preferably the moment of inertia is lessthan 0.43 oz.in² for a 1.680″ diameter golf ball. The moment of inertiafor oversized or enlarged golf balls, such as balls 1.70-1.72 inches indiameter, is also reduced.

The moment of inertia (i.e., “MOI”) of a golf ball (also known as“rotational inertia”) is the sum of the products formed by multiplyingthe mass (or sometimes the area) of each element of a figure by thesquare of its distance from a specified line such as the center of agolf ball. This property is directly related to the “radius of gyration”of a golf ball which is the square root of the ratio of the moment ofinertia of a golf ball about a given axis to its mass. It has been foundthat the lower the moment of inertia (or the closer the radius ofgyration is to the center of the ball) the higher the spin rate is ofthe ball with all other properties being held equally.

In all of the above aspects, the present invention is directed, in part,to decreasing the moment of inertia of a solid, non-wound, golf ball byvarying the weight arrangement and composition of the core (preferablythe inner spherical center core layer and the outer core layer). Byvarying the weight, size and density of the components of the golf ball,the moment of inertia of a golf ball can be decreased. Additionally,different types of matrix materials and/or crosslinking agents, or lackthereof, can be utilized in the core construction in order to produce anoverall solid, non-wound, golf ball exhibiting enhanced spin and feelwhile maintaining resiliency and durability.

In one other further aspect, the claimed subject matter of the presentapplication provides a multi-layered covered golf ball comprising a dualcore and a multi-layer cover. Again, the dual core comprises an innerhigh density spherical center core layer and at least one outer corelayer. The inner spherical center comprises a blend of high densitypowdered metal and/or other high density material and a first matrixmaterial selected from about a fifty percent / fifty percent blend ofpolybutadiene and polyisoprene. The spherical center has a specificgravity of greater than 1.2, such as from about 2.0 to about 20.0,preferably about 4.0 to 18.0, and most preferably, about 7.6-7.8 for a0.340″-0.344″ (8.6-8.75 mm) center.

At least one outer core layer of lower density is disposed about theinner spherical center. The outer core layer comprises a second matrixmaterial selected from thermosets, thermoplastics, and combinationsthereof.

The golf ball of this aspect also comprises a multi-layer cover havingat least an inner cover layer and outer cover layer. The inner coverlayer is disposed about the outer core layer. The outer cover layer isdisposed about and generally surrounds the inner cover layer. One ormore intermediate layers may also be included.

The golf balls of the present inventions having a high densityelastomeric nucleus, are more durable and softer than solid metalnucleus balls while increasing resiliency. The diameter of the center,or nucleus, is dependant upon the specific gravity of the chosen heavyweight filler and the first matrix material so that the maximum U.S.G.A.golf ball weight is not exceeded. The diameter range of the inner centeror nucleus is from about 0.200″ (about 5 mm) to a maximum of about0.830″ (21 mm), more preferably from about 0.300″ (about 7.6 mm) toabout 0.380″ (about 9.65 mm). The most preferred diameter is 11/32″, or0.340″ to 0.344″.

The density of the most preferred 0.340″ to 0.344″ center is less thanabout 20 grams/cc, preferably less than 12 grams/cc and most preferablyless than 8 grams/cc. The density is set so that it will not exceed theU.S.G.A. golf ball weight requirement. These and other objects andfeatures of the invention will be apparent from the followingdescription and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings which are presentedfor the purposes of illustrating the invention and not for the purposesof limiting the same.

FIG. 1 is a cross-sectional view of a golf ball in accordance with thepresent invention comprising a dual core component having a relativelysmall, high density spherical center comprising a powdered metal orother high density filler material dispersed in a first matrix materialcomprising polybutadiene and polyisoprene rubbers, a relatively thickouter core layer comprising a second matrix material selected fromthermosets, thermoplastics, or a combination thereof, and asingle-layered cover; and

FIG. 2 is a cross-sectional view of yet another embodiment golf ball inaccordance with the present invention comprising a dual core componenthaving a relatively small, high density spherical center comprising apowdered metal or other high density filler material dispersed in afirst matrix material comprising polybutadiene and polyisoprenesynthetic rubbers, a relatively thick outer core layer comprising asecond matrix material selected from thermosets, thermoplastics, or acombination thereof, an inner cover layer and an outer cover layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to improved solid, non-wound, golfballs comprising a polymeric core component with a high density center,or nucleus, and one or more outer core layers and a polymeric covercomponent with either a single or multi-layer cover. The golf balls ofthe present invention can be of standard or enlarged size. The ballspossess a desired combination of properties, including a highcoefficient of restitution (C.O.R.), a low moment of inertia, good sound(click) and feel, and a high spin rate on short iron shots.

In this regard, the moment of inertia, sometimes designated “MOI”herein, for the golf balls of the present invention is defined as thesum of the products formed by multiplying the mass of each element bythe square of its distance from a specified line or point. This is alsoknown as rotational inertia. Since the present invention golf ballscomprise a number of components, the MOI of the resulting golf ball isequal to the sum of the moments of inertia of each of its variouscomponents, taken about the same axis or point. All of the moments ofinertia of golf balls referred to herein are with respect to, or aretaken with regard to, the geometric center of the golf ball.

The term or designation “2×2” or “2×2 construction” as used hereinrefers to a golf ball construction utilizing two central corecomponents, e.g. a central core component and a core layer disposedabout the core component, and two cover components, e.g. a first innercover layer and a second outer cover layer. The present inventionhowever is not limited to 2×2 configurations and includes 2×1 (two corecomponents and a single cover component), 3×2 (three core components andtwo cover components), 2×3 configurations (two core components and threecover components), 3×3 configurations (three core components and threecover components), and additional configurations such as 4×2, 4×3, 4×4,2×4, 3×4, . . . etc.

The term “density reducing filler” as used herein refers to materialshaving relatively low densities, i.e. that are lightweight or have aspecific gravity less than the specific gravity of the basepolybutadiene rubber of 0.91. Examples of these materials includelightweight filler materials typically used to reduce the weight of aproduct in which they are incorporated. Specific examples include, forinstance, foams and other materials having a relatively large voidvolume. Typically, such filler materials have specific gravities lessthan 1.0.

The golf balls of the present invention utilize a unique dual ormulti-component core configuration. Preferably, the core comprises (i)an interior spherical center component formed from a blend including ahigh density filler material and a first matrix material comprisingpolybutadiene and polyisoprene and (ii) a core layer disposed about thespherical center component, the core layer formed from a second matrixmaterial such as a thermoset material, a thermoplastic material, orcombinations thereof. The cores may further comprise (iii) an optionalouter core layer disposed about the core layer. The outer core layer maybe formed from a third matrix material such as a thermoset material, athermoplastic material, or combinations thereof. The first, second orthird matrix materials can be of the same or different materials.

The high density center has a specific gravity of greater than 1.2 toabout 20.0, and preferably about 4.0 to 18.0, most preferably, 7.6-7.8for a 0.340″ to 0.344″ center. The weight of the remaining componentsare adjusted so that the ball will not exceed the U.S.G.A. golf ballweight requirement.

In this regard, the present invention is directed to golf ballscomprising a dual core component having a small, high density sphericalcenter comprising a powdered heavy metal filler or other high densityfiller material. These fillers have a specific gravity of 2.7 or more,preferably 7-8 or more, and most preferably 19.35. The high densityfiller is dispersed in a first matrix material selected from thermosets,thermoplastics, and combinations thereof.

Preferably, the blend of the high density metal filler materials and thefirst matrix material fails to contain any metal carboxylatecross-linking agents (i.e., metal salts of unsaturated fatty acids) suchas zinc diacrylate (ZDA) or zinc dimethyl acrylate (ZDMA).

A thick outer core layer is then disposed about the spherical center.The outer core layer comprises a second matrix material selected fromthermosets, thermoplastics, and combinations thereof. The outer diameterof the core is from about 1.25″ to 1.60″, and most preferably, 1.47″ to1.56″. A cover comprising one or more layers is subsequently moldedabout the dual core component to form a solid, non-wound golf ball.

In a particularly preferred form of the present invention, the golf ballcomprises a dual core assembly that includes a relatively small butheavy spherical center component, a thick but light core layer disposedabout the spherical center component, and a cover assembly disposedabout the dual core assembly. The heavy center of the core comprises (i)a polymeric material selected from one or more thermoset materials,thermoplastic materials or combinations thereof, and (ii) one or moreheavy weight powdered metals having a specific gravity of 2.7 or moredispersed throughout the polymeric material. Preferably, the heavycenter core is comprised of a blend of polybutadiene and polyisoprene.

The cover assembly may include a single cover or a multi-layered coverconfiguration. Preferably, the novel multi-layer golf ball covers of thepresent invention include a first or inner layer or ply of a high acid(greater than 16 weight percent acid) ionomer blend or a low acid (16weight percent acid or less) ionomer blend and second or outer layer orply comprised of a comparatively softer, low modulus ionomer, ionomerblend or other non-ionomeric thermoplastic or thermosetting elastomersuch as polyurethane or polyester elastomer. Most preferably, the innerlayer or ply includes a blend of low and/or high acid ionomers and has aShore D hardness of 58 or greater and the outer cover layer comprised ofionomer or polyurethane and has a Shore D hardness of at least 1 pointsofter than the inner layer.

Although the present invention is primarily directed to solid,non-wound, golf balls comprising a dual core component and a multi-layercover as described herein, the present invention also includes golfballs having a dual core component and conventional covers comprisingionomer, balata, various thermoplastic polyurethanes, castpolyurethanes, or any other cover materials capable of being crosslinkedvia radiation after cover molding.

Accordingly, the present invention is directed to golf balls having adual-core configuration and a single or multi-layer cover whichproduces, upon molding each layer around a high density inner center, agolf ball exhibiting enhanced spin and feel (i.e., lower compression)without adversely affecting the ball's resiliency (i.e., distance)and/or durability (i.e., cut resistance, scuff resistance, etc.)characteristics.

FIGS. 1 and 2 illustrate preferred embodiments of the golf balls inaccordance with the present invention. It will be understood that all ofthe figures referenced herein are schematic in nature and none of thereferenced figures are to scale. And so, the thicknesses and proportionsof the various layers and the diameter of the various core componentsare not necessarily as depicted.

The golf ball 8 comprises a single layer 11 (FIG. 1) or a multi-layeredcover 12 (FIG. 2) disposed about a core 10. The core 10 of the golf ballis formed (FIG. 2) of a small, high density spherical or center corelayer center 20 and a thick, low density outer core layer 22. The highdensity spherical center 20 is designed to produce a low moment ofinertia. This results, in part, in higher spin.

The multi-layered cover 12 (FIG. 2) comprises two layers: a first orinner layer or ply 14 and a second or outer layer or ply 16. The innerlayer 14 can be ionomer, ionomer blends, non-ionomer, non-ionomerblends, or blends of ionomer and non-ionomer. The outer layer 16 issofter than the inner layer and can be ionomer, ionomer blends,non-ionomer, non-ionomer blends or blends of ionomer and non-ionomer.

In a first multi-layered cover embodiment, the inner layer 14 iscomprised of a high acid (i.e. greater than 16 weight percent acid)ionomer resin or high acid ionomer blend. Preferably, the inner layer iscomprised of a blend of two or more high acid (i.e., at least 16 weightpercent acid) ionomer resins neutralized to various extents by differentmetal cations. The inner cover layer may or may not include a metalstearate (e.g., zinc stearate) or other metal fatty acid salt. Thepurpose of the metal stearate or other metal fatty acid salt is to lowerthe cost of production without affecting the overall performance of thefinished golf ball.

In a second multi-layered cover embodiment, the inner layer 14 iscomprised of a low acid (i.e., 16 weight percent acid or less) ionomerblend. Preferably, the inner layer is comprised of a blend of two ormore low acid (i.e., 16 weight percent acid or less) ionomer resinsneutralized to various extents by different metal cations. The innercover layer may or may not include a metal stearate (e.g., zincstearate) or other metal fatty acid salt.

It has been found that a hard inner layer in the multi-cover embodimentprovides for a substantial increase in resilience (i.e., enhanceddistance) over known multi-layer covered balls. The softer outer layeralong with the particular multi-component core of the present inventionprovides the desirable “feel” and high spin rate characteristic whilemaintaining the golf ball's resiliency. The soft outer layer allows thecover to deform more during impact and increases the area of contactbetween the club face and the cover, thereby imparting more spin on theball. As a result, the soft cover provides the ball with a balata-likefeel and playability characteristics with improved distance anddurability.

Consequently, the overall combination of the high density inner center,one or more outer core layers and the inner and outer cover layersresults in a golf ball having enhanced resilience (improved traveldistance) and durability (i.e., cut resistance, etc.) characteristicswhile maintaining, and in some instances, improving the playabilityproperties of the ball.

The specific components and characteristics of the solid, non-wound golfballs of the present invention are more particularly set forth below.

Core Assembly

As noted, the present invention golf balls utilize a unique dual coreconfiguration. Preferably, the cores comprise (i) an interior, highdensity, spherical center or center core layer component formed from afirst matrix material comprised of thermoset material, thermoplasticmaterial, or combinations thereof and (ii) an outer core layer disposedabout the spherical center component, the core layer being formed from asecond matrix material comprised of thermoset material, thermoplasticmaterial, or combinations thereof. Preferably the first matrix materialis a blend of polybutadiene and polyisoprene.

The spherical center component further comprises a blend of one or moreheavy weight metals and/or filler materials preferably in particulate orpowder form, dispersed throughout the thermoset or thermoplasticmaterial. Preferably, the blend is devoid of any metal carboxylatecross-linking agents.

The outer core layer is disposed immediately adjacent to, and inintimate contact with the center component. Specifically, one or moreouter core layer(s) is disposed about the center core layer. Mostpreferably, the outer core layer(s) is disposed immediately adjacent to,and in intimate contact with, the inner core layer(s). The matrixmaterial of the spherical center and the core layers may be of similaror different composition.

The core layers of the golf balls of the present invention generally aremore resilient than that of the cover layers, exhibiting a PGAcompression of about 85 or less, preferably about 30 to 85, and morepreferably about 40-60.

The core compositions and resulting molded core layers of the presentinvention are manufactured using relatively conventional techniques. Inthis regard, the core compositions of the invention preferably are basedon a variety of materials, particularly the conventional rubber basedmaterials such as cis-1,4 polybutadiene and mixtures of polybutadienewith other elastomers blended together with crosslinking agents, a freeradical initiator, specific gravity controlling fillers and the like.However, the use of metal carboxylate crosslinking agents are preferablynot included in the center sphere core layer.

Natural rubber, isoprene rubber, EPR, EPDM, styrene-butadiene rubber, orsimilar thermoset materials may be appropriately incorporated into thebase rubber composition of the butadiene rubber to form the rubbercomponent. It is preferred to use butadiene rubber as a base material ofthe composition for both the central core layer and the outer corelayer. Thus, the same rubber composition, including the rubber base,free radical initiator, and modifying ingredients, except for thespecific gravity controlling filler and crosslinking agent, can be usedin both the central and outer core layers. However, differentcompositions can readily be used in the different layers, includingthermoplastic materials such as a thermoplastic elastomer or athermoplastic rubber, or a thermoset rubber or thermoset elastomermaterial.

Some examples of materials suitable for use as an outer core layerinclude the above materials as well as polyether or polyesterthermoplastic urethanes, thermoset polyurethanes or metallocene polymersor blends thereof. For example, suitable metallocene polymers includefoams of thermoplastic elastomers based on metallocene single sitecatalyst based foams. Such metallocene based foam resins arecommercially available and are readily suitable for forming the outercore layer.

Examples of a thermoset material include a rubber based, castableurethane or a silicone rubber. The silicone elastomer may be anythermoset or thermoplastic polymer comprising, at least partially, asilicone backbone. Preferably, the polymer is thermoset and is producedby intermolecular condensation of silanols. A typical example is apolydimethylsiloxane crosslinked by free radical initiators, or by thecrosslinking of vinyl or allyl groups attached to the silicone throughreaction with silyhydride groups, or via reactive end groups. Thesilicone may include a reinforcing or non-reinforcing filler.Additionally, the present invention also contemplates the use of apolymeric foam material, such as the metallocene based foamed resin forthe outer core layers.

More particularly, a wide array of thermoset materials can be utilizedin the core components of the present invention. Examples of suitablethermoset materials include polybutadiene, polyisoprene,styrene/butadiene, ethylene propylene diene terpolymers, natural rubberpolyolefins, polyurethanes, silicones, polyureas, or virtually anyirreversibly cross-linkable resin system. It is also contemplated thatepoxy, phenolic, and an array of unsaturated polyester resins could beutilized.

The thermoplastic material utilized in the present invention golf ballsand, particularly their dual cores, may be nearly any thermoplasticmaterial. Examples of typical thermoplastic materials for incorporationin the golf balls of the present invention include, but are not limitedto, ionomers, polyurethane thermoplastic elastomers, and combinationsthereof. It is also contemplated that a wide array of otherthermoplastic materials could be utilized, such as polysulfones,polyamide-imides, polyarylates, polyaryletherketones, polyarylsulfones/polyether sulfones, polyether-imides, polyimides, liquidcrystal polymers, polyphenylene sulfides; and specialty high-performanceresins, which would include fluoropolymers, polybenzimidazole, andultrahigh molecular weight polyethylenes.

Additional examples of suitable thermoplastics include metallocenes,polyvinyl chlorides, polyvinyl acetates,acrylonitrile-butadiene-styrenes, acrylics, styrene-acrylonitriles,styrene-maleic anhydrides, polyamides (nylons), polycarbonates,polybutylene terephthalates, polyethylene terephthalates, polyphenyleneethers/polyphenylene oxides, reinforced polypropylenes, and high-impactpolystyrenes.

Preferably, the thermoplastic materials have relatively high meltingpoints, such as a melting point of at least about 300° F. Severalexamples of these preferred thermoplastic materials and which arecommercially available include, but are not limited to, Capron™ (a blendof nylon and ionomer), Lexan™ polycarbonate, Pebax®, and Hytrel™. Thepolymers or resin system may be cross-linked by a variety of means suchas by peroxide agents, sulphur agents, radiation or other cross-linkingtechniques, if applicable. However, the use of peroxide crosslinkingagents is generally preferred in the present invention.

Any or all of the previously described components in the cores of thegolf ball of the present invention may be formed in such a manner, orhave suitable fillers added, so that their resulting density isdecreased or increased. For example, heavy weight metals and/or fillermaterials are incorporated into the inner spherical center. This isdiscussed in more detail below.

Additionally, the outer core layers are formed or otherwise produced tobe light in weight. For instance, the components could be foamed, eitherseparately or in-situ. Related to this, a foamed light weight filleragent or density reducing filler may also be added to the outer corelayers.

The specially produced core components of the present invention aremanufactured using relatively conventional techniques. In this regard,the preferred core compositions (i.e., center, core layer, outer corelayer, etc.) of the invention may be based on polybutadiene, andmixtures of polybutadiene with other elastomers. It is preferred thatthe base elastomer have a relatively high molecular weight. The broadrange for the molecular weight of suitable base elastomers is from about50,000 to about 500,000. A more preferred range for the molecular weightof the base elastomer is from about 100,000 to about 500,000. As a baseelastomer for the core composition, cis-polybutadiene is preferablyemployed, or a blend of cis-polybutadiene with other elastomers such aspolyisoprene may also be utilized. Most preferably, cis-polybutadienehaving a weight-average molecular weight of from about 100,000 to about500,000 is employed. Along this line, it has been found that thecombination of a high cis-polybutadiene manufactured and sold by DowFrance 13131 Berre I'Etang Cedex, France, tradename Cariflex BR-1220,and a polyisoprene available from The Goodyear Tire & Rubber Co., Akron,Ohio, under the designation “Natsyn™ 2200” is particularly well suited.

Although the use of metal carboxylate crosslinking agents is notpreferred for the center core layer, these crosslinkers are included inthe additional outer core layers. The unsaturated carboxylic acidcomponent of the core composition (a co-crosslinking agent) is thereaction product of the selected carboxylic acid or acids and an oxideor carbonate of a metal such as zinc, magnesium, barium, calcium,lithium, sodium, potassium, cadmium, lead, tin, and the like.Preferably, the oxides of polyvalent metals such as zinc, magnesium andcadmium are used, and most preferably, the oxide is zinc oxide.

Exemplary of the unsaturated carboxylic acids which find utility in thepresent core compositions are acrylic acid, methacrylic acid, itaconicacid, crotonic acid, sorbic acid, and the like, and mixtures thereof.Preferably, the acid component is either acrylic or methacrylic acid.Usually, from about 12 to about 40, and preferably from about 15 toabout 35 parts by weight of the carboxylic acid salt, such as zincdiacrylate, is included in the outer core layers. The unsaturatedcarboxylic acids and metal salts thereof are generally soluble in theelastomeric base, or are readily dispersed.

The free radical initiator included in the core compositions is anyknown polymerization initiator (a co-crosslinking agent) whichdecomposes during the cure cycle. The term “free radical initiator” asused herein refers to a chemical which, when added to a mixture of theelastomeric blend and a metal salt of an unsaturated, carboxylic acid,promotes crosslinking of the elastomers by the metal salt of theunsaturated carboxylic acid. The amount of the selected initiatorpresent is dictated only by the requirements of catalytic activity as apolymerization initiator. Suitable initiators include peroxides,persulfates, azo compounds and hydrazides. Peroxides which are readilycommercially available are conveniently used in the present invention,generally in amounts of from about 0.5 to about 4.0 and preferably inamounts of from about 1.0 to about 3.0 parts by weight per each 100parts of elastomer and based on 40% active peroxide with 60% inertfiller.

Exemplary of suitable peroxides for the purposes of the presentinvention are dicumyl peroxide, n-butyl 4,4′-bis (butylperoxy) valerate,1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl peroxideand 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the like, as well asmixtures thereof. It will be understood that the total amount ofinitiators used will vary depending on the specific end product desiredand the particular initiators employed.

Examples of such commercially available peroxides are Luperco™ 230 or231 XL sold by Atochem, Lucidol Division, Buffalo, N.Y., and Trigonox™17/40 or 29/40 sold by Akzo Chemie America, Chicago, Ill. In this regardLuperco™ 230 XL and Trigonox™ 17/40 are comprised of n-butyl 4,4-bis(butylperoxy) valerate; and, Luperco™ 231 XL and Trigonox™ 14/40 arecomprised of 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane. The onehour half life of Luperco™ 231 XL is about 112° C., and the one hourhalf life of Trigonox™ 17/40 is about 129° C. Trigonox™ 42-40 B ispreferred and is chemically tert-Butyl peroxy-3,5,5, trimethylhexanoate.

The core compositions of the present invention may additionally containany other suitable and compatible modifying ingredients including, butnot limited to, metal oxides, fatty acids, and diisocyanates andpolypropylene powder resin. For example, Papi™ 94, a polymericdiisocyanate, commonly available from Dow Chemical Co., Midland, Mich.,is an optional component in the rubber compositions. It can range fromabout 0 to 5 parts by weight per 100 parts by weight rubber (phr)component, and acts as a moisture scavenger. In addition, it has beenfound that the addition of a polypropylene powder resin results in acore which is too hard (i.e. exhibits low compression) and thus allowsfor a reduction in the amount of crosslinking agent utilized to softenthe core to a normal or below normal compression.

Furthermore, because polypropylene powder resin can be added to the corecomposition without an increase in weight of the molded core uponcuring, the addition of the polypropylene powder allows for the additionof higher specific gravity fillers, such as mineral fillers. Since thecrosslinking agents utilized in the polybutadiene core compositions areexpensive and/or the higher specific gravity fillers are relativelyinexpensive, the addition of the polypropylene powder resinsubstantially lowers the cost of the golf ball cores while maintaining,or lowering, weight and compression.

The polypropylene (C₃H₅) powder suitable for use in the presentinvention has a specific gravity of about 0.90 g/cm³, a melt flow rateof about 4 to about 12 and a particle size distribution of greater than99% through a 20 mesh screen. Examples of such polypropylene powderresins include those sold by the Amoco Chemical Co., Chicago, Ill.,under the designations “6400 P”, “7000 P” and “7200 P”. Generally, from0 to about 25 parts by weight polypropylene powder per each 100 parts ofelastomer are included in the present invention.

Various activators may also be included in the compositions of thepresent invention. For example, zinc oxide, calcium oxide and/ormagnesium oxide are activators for the polybutadiene. The activator canrange from about 2 to about 30 parts by weight per 100 parts by weightof the rubbers (phr) component.

Fatty acids or metallic salts of fatty acids may also be included in thecompositions, functioning to improve moldability and processing.Generally, free fatty acids having from about 10 to about 40 carbonatoms, and preferably having from about 15 to about 20 carbon atoms, areused. Exemplary of suitable fatty acids are stearic acid and linoleicacids, as well as mixtures thereof. Exemplary of suitable metallic saltsof fatty acids include zinc stearate. When included in the corecompositions, the fatty acid component is present in amounts of fromabout 1 to about 25, preferably in amounts from about 2 to about 15parts by weight based on 100 parts rubber (elastomer).

It is preferred that the core compositions include zinc stearate as themetallic salt of a fatty acid in an amount of from about 2 to about 20parts by weight per 100 parts of rubber.

Diisocyanates may also be optionally included in the core compositions.The diisocyanates act here as moisture scavengers. When utilized, thediioscyanates are included in amounts of from about 0.2 to about 5.0parts by weight based on 100 parts rubber. Exemplary of suitablediisocyanates is 4,4′-diphenylmethane diisocyanate and otherpolyfunctional isocyanates know to the art.

Furthermore, the dialkyl tin difatty acids set forth in U.S. Pat. No.4,844,471, the dispersing agents disclosed in U.S. Pat. No. 4,838,556,and the dithiocarbamates set forth in U.S. Pat. No. 4,852,884 may alsobe incorporated into the polybutadiene compositions of the presentinvention. The specific types and amounts of such additives are setforth in the above identified patents, which are incorporated herein byreference.

The preferred core components of the invention are generally comprisedof 100 parts by weight of a base elastomer (or rubber) selected frompolybutadiene and mixtures of polybutadiene with other elastomers, suchas polyisoprene, 12 to 40 parts by weight of at least one metallic saltof an unsaturated carboxylic acid, and 0.5 to 4.0 parts by weight of afree radical initiator (40% active peroxide). However, as mentionedabove, the use of at least one metallic salt of an unsaturatedcarboxylic acid is preferably not included in the formulation of thehigh density center core layer.

In addition to polybutadiene, the following commercially availablethermoplastic resins are also particularly suitable for use in the noteddual cores employed in the golf balls of the present invention: Capron™8351 (available from Allied Signal Plastics), Lexan™ ML5776 (fromGeneral Electric), Pebax® 3533 (a polyether block amide from ElfAtochem), and Hytrel™ G4074 (a polyether ester from DuPont). Propertiesof these four thermoplastics are set forth below in Table 1.

TABLE 1 CAPRON ™ 8351 DAM 50% RH ASTM Test MECHANICAL Tensile Strength,Yield, psi (MPa) 7,800 (54) — D-638 Flexural Strength, psi (MPa) 9,500(85) — D-790 Flexural Modulus, psi (MPa) 230,000 (1,585) — D-790Ultimate Elongation, % 200 — D-638 Notched Izod Impact, ft-lbs/in (J/M)No Break — D-256 Drop Weight Impact, ft-lbs (J) 150 (200) — D-029 DropWeight Impact, @ ft-lbs (J) 150 (200) — D-3029 PHYSICAL Specific Gravity1.07 — D-792 THERMAL Melting Point, ° F. (° C.) 420 (215) — D-789 HeatDeflection @ 264 psi ° F. (° C.) 140 (60) — D-648 Lexan ™ ML5776PROPERTY TYPICAL DATA UNIT METHOD MECHANICAL Tensile Strength, yield,Type I, 0.125″ 8500 psi ASTM D 638 Tensile Strength, break, Type I,0.125″ 9500 psi ASTM D 638 Tensile Elongation, yield, Type I, 0.125″110.0 % ASTM D 638 Flexural Strength, yield, 0.125″ 12000 psi ASTM D 790Flexural Modulus, 0.125″ 310000 psi ASTM D 790 IMPACT Izod Impact,unnotched, 73 F. 60.0 ft-lb/in  ASTM D 4812 Izod Impact, notched, 73 F.15.5 ft-lb/in ASTM D 256 Izod Impact, notches 73 F., 0.250″ 12.0ft-lb/in ASTM D 256 Instrumented Impact Energy @ Peak, 73 F. 48.0 ft-lbs ASTM D 3763 THERMAL HDT, 284 psi, 0.250″, unannealed 257 deg F. ASTM D848 Thermal Index, Elec Prop 80 deg C. UL 7468 Thermal Index, Mech Propwith Impact 80 deg C. UL 7468 Thermal Index, Mech Prop without Impact 80deg C. UL 7468 PHYSICAL Specific Gravity, solid 1.19 — ASTM D 792 WaterAbsorption, 24 hours @ 73 F. 0.150 % ASTM D 570 Mold Shrinkage, flow,0.125″ 5.7 in/in E-3 ASTM D 955 Melt Flow Rate, nom'l, 300 C./1.2 kgf(0)7.5 g/10 min  ASTM D 1238 FLAME CHARACTERISTICS UL File Number, USAE121562 — 94HB Rated (tested thickness) 0.060 inch UL 94  PEBAX ® RESINSASTM TEST PROPERTY METHOD UNITS 3533 Specific Gravity D792 WaterAbsorption Equilibrium 0.5 (20° C., 50% R.H.>) 24 Hr. Immersion D570 1.2Hardness D2240 35D Tensile Strength, Ultimate D638 psi 5600 Elongation,Ultimate D638 % 580 Flexural Modulus D790 psi 2800 Izod Impact, NotchedD256 ft-lb./in. 20° C. NB −40° C. NB Abrasion Resistance D1044 Mg/1000104 H18/1000 g Cycles Tear Resistance Notched D624C lb/in. 260 MeltingPoint D3418 ° F. 306 Vicat Softening Point D1525 ° F. 165 HDT 66 psiD648 ° F. 115 Compression Set (24 hr., 160° F.) D395A % 54 HYTREL ™G4074 Thermoplastic Elastomer PHYSICAL Dens/Sp Gr ASTM D792 1.1800 sp gr23/23 C. Melt Flow ASTM D1238 5.20 @ E - 190 C./2.16 kg g/10/min Wat AbsASTM D570 2.100% MECHANICAL Elong @ Brk ASTM D638 230.0% Flex Mod ASTMD790 9500 psi TnStr @ Brk ASTM D638 2000 psi IMPACT Notch Izod ASTM D256No Break @ 73.0 F. @ 0.2500 inft-lb/in 0.50 @ −40.0 F. @ 0.2500inft-lb/in HARDNESS Shore ASTM D2240 40 Shore D THERMAL DTUL @ 66 ASTMD648 122 F. Melt Point 338.0 F. Vicat Soft ASTM D1525 248 F. Melt Point

In addition, various polyisoprenes may also be included in the corecomponents of the present invention. Examples of such polyisoprenes areas follows:

TRADENAME Composition ELASTOMER PROPERTIES Supplier Compounding &Processing Isolene Sp. gr. 0.92. Ash, 0.5-1.2%. Volatile matter,Depolymerzed 0.1% (24 hour at 300° F.), 100% rubber synthethic (flowableform). Grades: Isolene-40 (40,00 polyisoprene cps @ 100° F.; Mol wt. mw40,000); Isolene Hardman 75 viscosity (75,000 cps @ 100° F.); DPR- 400viscosity (400,000 @ 100° F., mol wt. mw 40,000). Gardner color (60-8)Natsyn 2200 Sp. gr. 0.91. White, non-staining, solution Goodyearpolymerized, IR with excellent uniformity R. T. Vanderbilt and purity.Vulcanized with conventional cure systems, Mooney visc (ml-4 @ 212° F.).70-90, needs little or no breakdown. Tg. 98° F. Natsyn 2205 Sp. gr.0.91. White, non-staining, virtually DuPont gel free solutionpolymerized IR. Mooney R.T. Vanderbilt viscosity (ml-4 @ 212° F.).70-90, needs little or no breakdown. Tg. 98° F. Natsyn 2210 Sp. gr.0.91. White, non-staining, low DuPont Mooney, solution polymerized, IRwith R.T. Vanderbllt excellent uniformity and purity. Vulcanized withconventional cure systems, Mooney visc (ml-4 @ 212° F.) 50-65, thereforeno breakdown is required. Tg-98°. Nipol IR 2200L Sp. gr. 0.92, Mooneyvisc. ml-4 at 100° C. Goldsmith & Eggleton 70, Cis 1,498%. non-staining.SKI-3 Staining IR: 97.5 ds 1,4; Mooney viscosity, Polyisopnene density915 ± 5. HA. Astlett SKI-3 Mooney visc. MB 1 = 4 (100° C.) 65-85;Isoprene Rubber Plasticity 0.300.41; ultimate elongation, % Nizh USAmin. 800; Ultimate tensile strength MPa (kgF/sq.cm.) min at 23° C. 30.4at 100° C. 21.6. SKI-3 (Russian IR) Staining IR, 97.5 cis 1,4. 60 MooneyPolyisoprene viscosity, density 915 ± 5. Alcan SKI-3-S Non-staining 97.5ds 1,4 73 ± 7 Mooney Polyisoprene viscosity, density 915 ± 5. H.A.Astlett SKI-3-S (Russian IR) Non-staining 97.5 cis 1,4 73 ± 7 MooneyPolyisoprene viscosity, density 915 ± 5. Alcan

The inner spherical center preferably can be compression or transfermolded from an uncured or lightly cured elastomer composition. Toachieve higher coefficients of restitution and/or to increase hardnessin the core, the manufacturer may include a small amount of a metaloxide such as zinc oxide. Non-limiting examples of other materials whichmay be used in the core composition including compatible rubbers orionomers, and low molecular weight fatty acids such as stearic acid.Free radical initiator catalysts such as peroxides are admixed with thecore composition so that on the application of heat and pressure, acuring or cross-linking reaction takes place.

Also included in the matrix materials of the inner spherical centers,are one or more heavy weight fillers or powder materials. Such an innerspherical center exhibits a lower moment of inertia than conventionaltwo-piece golf balls. The moment of inertia for the present golf ball isless than 0.45 oz.in² and more preferably less than 0.44 oz.in². Mostpreferably, the moment of inertia for the golf ball of the presentinvention is less than 0.43 oz.in².

The powdered metal in the spherical center may be in a wide array oftypes, geometries, forms, and sizes. The powdered metal may be of anyshape so long as the metal may be blended with the other componentswhich form the spherical center.

Particularly, the metal may be in the form of metal particles, metalflakes, and mixtures thereof. However, again, the forms of powderedmetal are not limited to such forms. The metal may be in a form having avariety of sizes so long as the objectives of the present invention aremaintained. Preferably, the powdered metal is incorporated into thematrix material of the spherical center in finely defined form, as forexample, in a size generally less than about 20 mesh, preferably lessthan about 200 mesh and most preferably less than about 325 mesh, U.S.standard size. The amount of powdered metal included in the sphericalcenter is dictated by weight restrictions, the type of powdered metal,and the overall characteristics of the finished ball. However, theamount of powdered metal is generally from about 100 to about 3200 partsby weight matrix material, more preferably, from about 500 to about 1500matrix material and most preferably from about 1200 to 1400 matrixmaterial for a 0.340″ diameter polybutadiene center.

The spherical center may include more than one type of powdered metal.Particularly, the spherical center may include blends of the powderedmetals disclosed in Table 2 below. The blends of powdered metals may bein any proportion with respect to each other in order for the sphericalcenter and golf ball to exhibit the characteristics noted herein.

In this regard, the weight of the inner spherical core component isincreased in the present invention through the inclusion of 100-3200parts per hundred parts matrix material of metal particles and otherheavy weight filler materials. As used herein, the term “heavy weightfiller materials” is defined as any material having a specific gravitygreater than 2.7. Preferably, the particles (or flakes, fragments,fibers, etc.) of powdered metal are added to the inner spherical core inorder to decrease the moment of inertia of the ball without affectingthe ball's feel and durability characteristics.

The inner spherical core is filled with one or more reinforcing ornon-reinforcing heavy weight fillers such as metal (or metal alloy)powders. Representatives of such metal (or metal alloy) powders includebut are not limited to, tungsten powder, bismuth powder, boron powder,brass powder, bronze powder, cobalt powder, copper powder, inconnelmetal powder, iron metal powder, molybdenium powder, nickel powder,stainless steel powder, titanium metal powder, zirconium oxide powder,aluminum flakes, and aluminum tadpoles.

Examples of several suitable powdered metals which can be included inthe present invention are as follows:

TABLE 2 Metals and Alloys (Powders) Specific Gravity titanium 4.51tungsten 19.35 bismuth 9.78 nickel 8.90 molybdenum 10.2 iron 7.86 copper8.94 brass 8.2-8.4 bronze 8.70-8.74 cobalt 8.92 zinc 7.14 tin 7.31aluminum 2.70

The amount and type of powdered metal utilized is dependent upon theoverall characteristics of the high spinning, soft feeling, golf balldesired. Generally, lesser amounts of high specific gravity powderedmetals are necessary to produce a decrease in the moment of inertia incomparison to low specific gravity materials. Furthermore, handling andprocessing conditions can also effect the type of heavy weight powderedmetals incorporated into the spherical center. In this regard,Applicants have found that the inclusion of approximately 1200-1400 phrtungsten powder into the inner spherical center produces the desiredincrease in the moment of inertia without involving substantialprocessing changes. Thus, 1200-1400 phr tungsten powder is the mostpreferred heavy filler material at the time of this writing for a 0.340″diameter polybutadiene center or nucleus.

Furthermore, powdered iron can also be preferably blended with powderedtungsten or other powdered materials in the spherical center so that thespherical center can be attracted to a magnet. The magnetic attractionallows for automated assembly of the spherical center to the remaininglayers in forming the golf ball. Preferably, the powdered iron is about4-10% by weight of the spherical center composition when used as anattraction agent for a magnet.

The powdered metal constitutes at least 50% by weight of the totalspherical center composition. Preferably, the powdered metal constitutesat least 60% of the spherical center composition. Most preferably, thepowdered metal constitutes at least 70% of the spherical centercomposition.

When the preferred high density powdered metal comprises the sphericalcenter, the diameter of the spherical center can vary considerably solong as the maximum U.S.G.A. golf ball weight is not exceeded.Preferably, the spherical center has a diameter in the range of about0.200 inches to about 0.830 inches. More preferably, the diameter of thespherical center is from about 0.200 inches to about 0.400 inches, mostpreferably from about 0.300 inches to about 0.380 inches, with0.340-0.344 inches being optimal.

The spherical center comprising a high density powdered metal has adensity that will not exceed the U.S.G.A. golf ball weight requirement.Preferably, the density is no more than about 12-20, preferably lessthan 9 grams/cm³ for a 0.340″-0.344″ diameter nucleus.

The outer diameter of the center core and the outer diameter of theouter core (core diameter) may vary. However, the center core has adiameter of about 5 to 21 mm and preferably about 5 to 15 mm while theouter core has a diameter of about 30 to 40 mm and preferably 35 to 38mm, depending on the size of the center core and the finished size ofthe ball. Typically the center core diameter is about 5 to 12 mm.

The core having a two-layer structure composed of the inner core and theouter core is referred to as the solid core in the present invention.The above expression is in contrast to a thread-wound core (core formedby winding a rubber thread around the center portion which is solid orfilled with a liquid material).

The double cores of the inventive golf balls typically have acoefficient of restitution of about 0.730 or more, more preferably 0.770or more and a PGA compression of about 95 or less, and more preferably70 or less. The double cores have a weight of 25 to 40 grams andpreferably 30 to 40 grams and a Shore C hardness of less than 80, withthe preferred Shore C hardness being about 50 to 75.

As mentioned above, the present invention includes golf ball embodimentsthat utilize two or more core components. For example, in accordancewith the present invention, a core assembly is provided that comprises acentral core component and one or more core layers disposed about thecentral core component. Details for the second and third or more corelayers are also included herein in the description of the core layerutilized in a dual core configuration.

In producing golf ball centers utilizing the present compositions, theingredients may be intimately mixed using, for instance, two roll millsor a Banbury™ mixer until the composition is uniform, usually over aperiod of from about 5 to about 20 minutes. The sequence of addition ofcomponents is not critical. A preferred blending sequence is describedbelow.

The matrix material or elastomer, powdered metal zinc salt (if desired),the high specific gravity additive such as powdered metal, metal oxide,fatty acid, and the metallic dithiocarbamate (if desired), surfactant(if desired), and tin difatty acid (if desired), are blended for about 7minutes in an internal mixer such as a Banbury™ mixer. As a result ofshear during mixing, the temperature rises to about 200° F. The mixingis desirably conducted in such a manner that the composition does notreach incipient polymerization temperatures during the blending of thevarious components. The initiator and diisocyanate are then added andthe mixing continued until the temperature reaches about 220° F.whereupon the batch is discharged onto a two roll mill, mixed for aboutone minute and sheeted out.

The sheet is rolled into a “pig” and then placed in a Barwell™ preformerand slugs of the desired weight are produced. The slugs to be used forthe center core layer are then subjected to compression molding at about140° C. to about 170° C. for about 10 to 50 minutes. Note that thetemperature in the molding process is not always required to beconstant, and may be changed in two or more steps. In fact, the slugsfor the outer core layer are frequently preheated for about one halfhour at about 75° C. prior to molding. After molding, the molded centersare cooled, the cooling effected at room temperature for about 4 hoursor in cold water for about one hour. The molded centers are subjected toa centerless grinding operation whereby a thin layer of the molded coreis removed to produce a round center. Alternatively, the centers areused in the as-molded state with no grinding needed to achieveroundness.

The solid inner centers are generally from 0.200 to 0.830 inches indiameter, preferably 0.300 to 0.380 inches, and most preferably 0.320 to0.360 inches, with a weight of 1.2 grams to 5.9 grams, preferably 1.8 to3.6 grams, and most preferably 2.6 to 3.0 grams for a 0.340″-0.344″diameter nucleus. The specific gravity of the inner spherical center isfrom 1.2 to 20.0, preferably 5 to 12, and most preferably 7.6 to 7.9 fora 0.340″-0.344″ diameter nucleus.

The center is converted into a dual core by providing at least one layerof core material thereon, ranging in thickness from about 0.69 to about0.38 inches and preferably from about 0.65 to about 0.60 inches. Theouter core layers may be of similar or different matrix material as thespherical center. Preferably the outer core layer comprisespolybutadiene which has been weight adjusted to compensate for the heavyweight spherical center.

The outer core layer can be applied around the spherical center byseveral different types of molding processes. For example, thecompression molding process for forming the cover layer(s) of a golfball that is set forth in U.S. Pat. No. 3,819,795 can be adapted for usein producing the core layer(s) of the present invention.

In such a modified process, preforms or slugs of the outer corematerial, i.e., the thermoset material utilized to form the outer corelayer, are placed in the upwardly open, bottom cavities of a lower moldmember of a compression molding assembly, such as a conventional golfball or core platen press. The upwardly facing hemispherical cavitieshave inside diameters substantially equal to the finished core to beformed. In this regard, the inside diameters of the cavities areslightly larger (i.e., approximately 0.010″ diameter) than the desiredfinished core size in order to account for material shrinkage.

An intermediate mold member comprising a center Teflon®-coated platehaving oppositely-affixed hemispherical protrusions extending upwardlyon the upper surface and extending downwardly on the lower surface, eachhemispherical protrusion about 0.340 inches in diameter, is placed overthe lower mold member and on top of the preforms located in the bottommolding cavities. The size and outside diameters of the hemisphericalprotrusions are substantially equal to the centers to be utilized andthus can vary with the various sizes of the centers to be used.

Additional preforms of the same outer core material are subsequentlyplaced on top of the upperly-projecting 0.340″ hemispherical protrusionsaffixed to the upper surfaces of the Teflon®-coated plate of theintermediate mold member. The additional preforms are then covered bythe downwardly open cavities of the top mold member. Again the downwardfacing cavities of the top mold member have inside diameterssubstantially equal to the core to be formed.

Specifically, the bottom mold member is engaged with the top mold memberwith the intermediate mold member having the oppositely protrudinghemispheres being present in the middle of the assembly. The moldmembers are then compressed together to form hemispherical core halves.

In this regard, the mold assembly is placed in a press and cold formedat room temperature using approximately 10 tons of pressure in a steampress. The molding assembly is closed and heated below the cureactivation temperature of about 150° F. for approximately four minutesto soften and mold the outer core layer materials. While still undercompression, but at the end of the compression cycle, the mold membersare water cooled to a temperature to less than 100° F. in order tomaintain material integrity for the final molding step. This coolingstep is beneficial since cross linking has not yet proceeded to provideinternal chemical bonds to provide full material integrity. Aftercooling, the pressure is released.

The molding assembly is then opened, the upper and lower mold membersare separated, and the intermediate mold member is removed whilemaintaining the formed outer core layer halves in their respectivecavities. Each of the halves has an essentially perfectly formedone-half shell cavity or depression in its uncured thermoset material.These one-half shell cavities or depressions were produced by thehemispherical protrusions of the intermediate mold member.

Previously molded centers of about 0.340″ in diameter, are then placedinto the bottom cavities or depressions of the uncured thermosetmaterial. The top portion of the molding assembly is subsequentlyengaged with the bottom portion and the material that is disposedtherebetween is cured for about 12 minutes at about 320° F. Those ofordinary skill in the art relating to free radical curing agents forpolymers are conversant with adjustments of cure times and temperaturesrequired to effect optimum results with any specific free radical agent.The combination of the high temperature and the compression force joinsthe core halves, and bonds the cores to the center. This process resultsin a substantially continuously outer core layer being formed around thecenter component.

In an alternative, and in some instances, more preferable compressionmolding process, the Teflon®-coated plate of the intermediate moldmember has only a set of downwardly projecting hemispherical protrusionsand no oppositely affixed upwardly-projecting hemispherical protrusions.Substituted for the upwardly-projecting protrusions are a plurality ofhemispherical recesses in the upper surface of the plate. Each recess islocated in the upper surface of the plate opposite a protrusionextending downwardly from the lower surface. The recess has an insidediameter substantially equal to the center to be utilized and isconfigured to receive the bottom half of the center.

The previously molded centers of about 0.340″ in diameter are thenplaced in the cavities located on the upper surface of the plate of theintermediate mold member. Each of the centers extends above the uppersurface of the plate of the intermediate mold member and is pressed intothe lower surface of the upper preform when the molds are initiallybrought together during initial compression.

The molds are then separated and the plate removed, with the centersbeing retained (pressed into) the half shells of the upper preforms.Mating cavities or depressions are also formed in the half shells of thelower preforms by the downwardly projecting protrusions of theintermediate mold member. With the plate now removed, the top portion ofthe molding assembly is then joined with the bottom portion. In sodoing, the centers projecting from the half shells of the upper performsenter into the cavities or depressions formed in the half shells of thelower preforms. The material included in the molds is subsequentlycompressed, treated and cured as stated above to form a golf ball corehaving a centrally located center and an outer core layer. This processcan continue for additional added core layers.

After molding, the core comprising a centrally located center surroundedby at least one outer core layer is removed from the mold and thesurface thereof preferably is treated to facilitate adhesion thereof tothe covering materials. Surface treatment can be effected by any of theseveral techniques known in the art, such as corona discharge, ozonetreatment, sand blasting, brush tumbling, and the like. Preferably,surface treatment is effected by grinding with an abrasive wheel.

Cover Assembly

A. Multi-Covers

i. Inner Cover Layer

The inner cover layer is harder than the outer cover layer and generallyhas a thickness in the range of 0.01 to 0.10 inches, preferably 0.03 to0.07 inches for a 1.68 inch ball and 0.05 to 0.10 inches for a 1.72 inch(or more) ball. The core and inner cover layer together form an innerball having a coefficient of restitution of 0.780 or more and morepreferably 0.790 or more, and a diameter in the range of 1.48-1.64inches for a 1.68 inch ball and 1.50-1.70 inches for a 1.72 inch (ormore) ball. The inner cover layer has a Shore D hardness of 60 or more.It is particularly advantageous if the golf balls of the invention havean inner layer with a Shore D hardness of 65 or more. Theabove-described characteristics of the inner cover layer provide aninner ball having a PGA compression of 100 or less. It is found thatwhen the inner ball has a PGA compression of 90 or less, excellentplayability results.

The inner layer compositions include the high acid ionomers such asthose developed by E.I. DuPont de Nemours & Company under the trademark“Surlyn®” and by Exxon Corporation under the trademark “Escor™” or tradename “Iotek”, or blends thereof. Examples of compositions which may beused as the inner layer herein are set forth in detail in a continuationof U.S. application Ser. No. 08/174,765, which is a continuation of U.S.application Ser. No. 07/776,803 filed Oct. 15, 1991, and Ser. No.08/493,089, which is a continuation of Ser. No. 07/981,751, which inturn is a continuation of Ser. No. 07/901,660 filed Jun. 19, 1992, allof which are incorporated herein by reference. Of course, the innerlayer high acid ionomer compositions are not limited in any way to thosecompositions set forth in said applications.

The high acid ionomers which may be suitable for use in formulating theinner layer compositions are ionic copolymers which are the metal, i.e.,sodium, zinc, magnesium, etc., salts of the reaction product of anolefin having from about 2 to 8 carbon atoms and an unsaturatedmonocarboxylic acid having from about 3 to 8 carbon atoms. Preferably,the ionomeric resins are copolymers of ethylene and either acrylic ormethacrylic acid. In some circumstances, an additional comonomer such asan acrylate ester (i.e., iso- or n-butylacrylate, etc.) can also beincluded to produce a softer terpolymer. The carboxylic acid groups ofthe copolymer are partially neutralized (i.e., approximately 10-100%,preferably 30-70%) by the metal ions. Each of the high acid ionomerresins which may be included in the inner layer cover compositions ofthe invention contains greater than about 16% by weight of a carboxylicacid, preferably from about 17% to about 25% by weight of a carboxylicacid, more preferably from about 18.5% to about 21.5% by weight of acarboxylic acid.

Although the inner layer cover composition of several embodiments of thepresent invention preferably includes a high acid ionomeric resin, thescope of the patent embraces all known high acid ionomeric resinsfalling within the parameters set forth above, only a relatively limitednumber of these high acid ionomeric resins have recently becomecommercially available.

The high acid ionomeric resins available from Exxon under thedesignation “Escor™” and or “Iotek”, are somewhat similar to the highacid ionomeric resins available under the “Surlyn®” trademark. However,since the Escor™/Iotek ionomeric resins are sodium or zinc salts ofpoly(ethylene-acrylic acid) and the “Surlyn®” resins are zinc, sodium,magnesium, etc. salts of poly(ethylene-methacrylic acid), distinctdifferences in properties exist.

Examples of the high acid methacrylic acid based ionomers found suitablefor use in accordance with this invention include Surlyn®8220 and 8240(both formerly known as forms of Surlyn® AD-8422), Surlyn9220 (zinccation), Surlyn®SEP-503-1 (zinc cation), and Surlyn®SEP-503-2 (magnesiumcation). According to DuPont, all of these ionomers contain from about18.5 to about 21.5% by weight methacrylic acid.

More particularly, Surlyn® AD-8422 is currently commercially availablefrom DuPont in a number of different grades (i.e., AD-8422-2, AD-8422-3,AD-8422-5, etc.) based upon differences in melt index. According toDuPont, Surlyn® 8422, which is believed recently to have beenredesignated as 8220 and 8240, offers the following general propertieswhen compared to Surlyn® 8920, the stiffest, hardest of all on the lowacid grades (referred to as “hard” ionomers in U.S. Pat. No. 4,884,814):

LOW ACID HIGH ACID (15 wt % Acid) (>20 wt % Acid) SURLYN ® SURLYN ®SURLYN ® 8920 8422-2 8422-3 IONOMER Cation Na Na Na Melt Index 1.2 2.81.0 Sodium, Wt % 2.3 1.9 2.4 Base Resin MI 60 60 60 MP¹, ° C. 88 86 85FP¹, ° C. 47 48.5 45 COM- PRESSION MOLDING² Tensile Break, 4350 41905330 psi Yield, psi 2880 3670 3590 Elongation, % 315 263 289 Flex Mod,53.2 76.4 88.3 K psi Shore D 66 67 68 hardness ¹DSC second heat, 10°C./min heating rate. ²Samples compression molded at 150° C. annealed 24hours at 60° C. 8422-2, -3 were homogenized at 190° C. before molding.

In comparing Surlyn® 8920 to Surlyn® 8422-2 and Surlyn® 8422-3, it isnoted that the high acid Surlyn® 8422-2 and 8422-3 ionomers have ahigher tensile yield, lower elongation, slightly higher Shore D hardnessand much higher flexural modulus. Surlyn® 8920 contains 15 weightpercent methacrylic acid and is 59% neutralized with sodium.

In addition, Surlyn®SEP-503-1 (zinc cation) and Surlyn®SEP-503-2(magnesium cation) are high acid zinc and magnesium versions of theSurlyn®AD 8422 high acid ionomers. When compared to the Surlyn® AD 8422high acid ionomers, the Surlyn® SEP-503-1 and SEP-503-2 ionomers can bedefined as follows:

Surlyn ® Ionomer Ion Melt Index Neutralization % AD 8422-3 Na 1.0 45 SEP503-1 Zn 0.8 38 SEP 503-2 Mg 1.8 43

Further, Surlyn® 8162 is a zinc cation ionomer resin containingapproximately 20% by weight (i.e., 18.5-21.5% weight) methacrylic acidcopolymer that has been 30-70% neutralized. Surlyn® 8162 is currentlycommercially available from DuPont.

Examples of the high acid acrylic acid based ionomers suitable for usein the present invention also include the Escor™ or Iotek high acidethylene acrylic acid ionomers produced by Exxon such as Ex 1001, 1002,959, 960, 989, 990, 1003, 1004, 993, 994. In this regard, Escor™ orIotek 959 is a sodium ion neutralized ethylene-acrylic neutralizedethylene-acrylic acid copolymer. According to Exxon, Ioteks 959 and 960contain from about 19.0 to 21.0% by weight acrylic acid withapproximately 30 to about 70 percent of the acid groups neutralized withsodium and zinc ions, respectively. The physical properties of thesehigh acid acrylic acid based ionomers are set forth in Tables 3 and 4 asfollows:

TABLE 3 Physical Properties of Various Ionomers ESCOR ™ ESCOR ™ Ex Ex(IOTEK) Ex Ex (IOTEK) PROPERTY 1001 1002 959 1003 1004 960 Melt index, 1.0  1.6    2.0  1.1  2.0    1.8 g/10 min Cation Na Na Na Zn Zn ZnMelting 183   183   172 180   180.5 174 Point, ° F. Vicat 125   125  130 133   131   131 Softening Point, ° F. Tensile  34.4  22.5 4600  24.8  20.6 3500  @ Break MPa MPa psi MPa MPa psi Elongation 341   348  325 387   437   430 @ Break, % Hardness, 63  62   66 54  53   57 Shore DFlexural 365   380   66,000    147   130   27,000    Modulus MPa MPa psiMPa MPa psi

TABLE 4 Physical Properties of Various Ionomers EX 989 EX 993 EX 994 EX990 Melt index g/10 min 1.30 1.25 1.32 1.24 Moisture ppm 482 214 997 654Cation type — Na Li K Zn M+ content by AAS wt % 2.74 0.87 4.54 0 Zncontent by AAS wt % 0 0 0 3.16 Density kg/m³ 959 945 976 977 Vicatsoftening point ° C. 52.5 51 50 55.0 Crystallization point ° C. 40.139.8 44.9 54.4 Melting point ° C. 82.6 81.0 80.4 81.0 Tensile at yieldMPa 23.8 24.6 22 16.5 Tensile at break MPa 32.3 31.1 29.7 23.8Elongation at break % 330 260 340 357 1% secant modulus MPa 389 379 312205 Flexural modulus MPa 340 368 303 183 Abrasion resistanoe mg 20.0 9.215.2 20.5 Hardness Shore D — 62 62.5 61 56 Zwick Rebound % 61 63 59 48

Furthermore, as a result of the development by the assignee of thisapplication of a number of new high acid ionomers neutralized to variousextents by several different types of metal cations, such as bymanganese, lithium, potassium, calcium and nickel cations, several newhigh acid ionomers and/or high acid ionomer blends besides sodium, zincand magnesium high acid ionomers or ionomer blends are now available forgolf ball cover production. It has been found that these new cationneutralized high acid ionomer blends produce inner cover layercompositions exhibiting enhanced hardness and resilience due tosynergies which occur during processing. Consequently, the metal cationneutralized high acid ionomer resins recently produced can be blended toproduce substantially higher C.O.R.'s than those produced by the lowacid ionomer inner cover compositions presently commercially available.

More particularly, several new metal cation neutralized high acidionomer resins have been produced by the assignee by neutralizing, tovarious extents, high acid copolymers of an alpha-olefin and an alpha,beta-unsaturated carboxylic acid with a wide variety of different metalcation salts. This discovery is the subject matter of U.S. Pat. No.5,688,869, incorporated herein by reference. It has been found thatnumerous new metal cation neutralized high acid ionomer resins can beobtained by reacting a high acid copolymer (i.e., a copolymer containinggreater than 16% by weight acid, preferably from about 17 to about 25weight percent acid, and more preferably about 20 weight percent acid),with a metal cation salt capable of ionizing or neutralizing thecopolymer to the extent desired (i.e., from about 10% to 90%).

The base copolymer is made up of greater than 16% by weight of an alpha,beta-unsaturated carboxylic acid and an alpha-olefin. Optionally, asoftening comonomer can be included in the copolymer. Generally, thealpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene,and the unsaturated carboxylic acid is a carboxylic acid having fromabout 3 to 8 carbons. Examples of such acids include acrylic acid,methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid,maleic acid, fumaric acid, and itaconic acid, with acrylic acid beingpreferred.

The softening comonomer that can be optionally included in the innercover layer for the golf ball of the invention may be selected from thegroup consisting of vinyl esters of aliphatic carboxylic acids whereinthe acids have 2 to 10 carbon atoms, vinyl ethers wherein the alkylgroups contains 1 to 10 carbon atoms, and alkyl acrylates ormethacrylates wherein the alkyl group contains 1 to 10 carbon atoms.Suitable softening comonomers include vinyl acetate, methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate,butyl methacrylate, or the like.

Consequently, examples of a number of copolymers suitable for use toproduce the high acid ionomers included in the present inventioninclude, but are not limited to, high acid embodiments of anethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer,an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer,an ethylene/methacrylic acid/vinyl acetate copolymer, anethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymerbroadly contains greater than 16% by weight unsaturated carboxylic acid,from about 39 to about 83% by weight ethylene and from 0 to about 40% byweight of a softening comonomer. Preferably, the copolymer containsabout 20% by weight unsaturated carboxylic acid and about 80% by weightethylene. Most preferably, the copolymer contains about 20% acrylic acidwith the remainder being ethylene.

Along these lines, examples of the preferred high acid base copolymerswhich fulfill the criteria set forth above, are a series ofethylene-acrylic copolymers which are commercially available from TheDow Chemical Company, Midland, Mich., under the “Primacor™” designation.These high acid base copolymers exhibit the typical properties set forthbelow in Table 5.

TABLE 5 Typical Properties of Primacor Ethylene-Acrylic Acid CopolymersFLEXURAL VICAT PERCENT DENSITY, MELT INDEX, TENSILE MODULUS SOFT SHORE DGRADE ACID g/cc g/10 min YD. ST (psi) (psi) PT (° C.) HARDNESS ASTMD-792 D-1238 D-638 D-790 D-1525 D-2240 5980 20.0 0.958  300.0 — 4800 4350 5990 20.0 0.955 1300.0 650 2600- 40 42 3200 5981 20.0 0.960  300.0900 3200 46 48 5983 20.0 0.958  500.0 850 3100 44 45 5991 20.0 0.9532600.0 635 2600 38 40 ¹The Melt Index values are obtained according toASTM D-1238, at 190° C.

Due to the high molecular weight of the Primacor 5981 grade of theethylene-acrylic acid copolymer, this copolymer is the more preferredgrade utilized in the invention.

The metal cation salts utilized in the invention are those salts whichprovide the metal cations capable of neutralizing, to various extents,the carboxylic acid groups of the high acid copolymer. These includeacetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium,potassium, nickel, magnesium, and manganese.

Examples of such lithium ion sources are lithium hydroxide monohydrate,lithium hydroxide, lithium oxide and lithium acetate. Sources for thecalcium ion include calcium hydroxide, calcium acetate and calciumoxide. suitable zinc ion sources are zinc acetate dihydrate and zincacetate, a blend of zinc oxide and acetic acid. Examples of sodium ionsources are sodium hydroxide and sodium acetate. Sources for thepotassium ion include potassium hydroxide and potassium acetate.Suitable nickel ion sources are nickel acetate, nickel oxide and nickelhydroxide. Sources of magnesium include magnesium oxide, magnesiumhydroxide, magnesium acetate. Sources of manganese include manganeseacetate and manganese oxide.

The new metal cation neutralized high acid ionomer resins are producedby reacting the high acid base copolymer with various amounts of themetal cation salts above the crystalline melting point of the copolymer,such as at a temperature from about 200° F. to about 500° F., preferablyfrom about 250° F. to about 350° F., under high shear conditions at apressure of from about 10 psi to 10,000 psi. Other well known blendingtechniques may also be used. The amount of metal cation salt utilized toproduce the new metal cation neutralized high acid based ionomer resinsis the quantity which provides a sufficient amount of the metal cationsto neutralize the desired percentage of the carboxylic acid groups inthe high acid copolymer. The extent of neutralization is generally fromabout 10% to about 90%.

As indicated below in Table 6 and more specifically in Example 1 in U.S.application Ser. No. 08/493,089, a number of new types of metal cationneutralized high acid ionomers can be obtained from the above indicatedprocess. These include new high acid ionomer resins neutralized tovarious extends with manganese, lithium, potassium, calcium and nickelcations. In addition, when a high acid ethylene/acrylic acid copolymeris utilized as the base copolymer component of the invention and thiscomponent is subsequently neutralized to various extents with the metalcation salts producing acrylic acid based high acid ionomer resinsneutralized with cations such as sodium, potassium, lithium, zinc,magnesium, manganese, calcium and nickel, several new cation neutralizedacrylic acid based high acid ionomer resins are produced.

TABLE 6 Metal Cation Neutralized High Acid Ionomers Formulation Wt-%Wt-% Melt Shore D No. Cation Salt Neutralization Index C.O.R. Hardness1(NaOH) 6.98 67.5 0.9 0.804 71 2(NaOH) 5.66 54 2.4 0.808 73 3(NaOH) 3.8435.9 12.2 0.812 69 4(NaOH) 2.91 27 17.5 0.812 (brittle) 5(MnAc) 19.671.7 7.5 0.809 73 6(MnAc) 23.1 88.3 3.5 0.814 77 7(MnAc) 15.3 53 7.50.81  72 B(MnAc) 26.5 106 0.7 0.813 (brittle) 9(LiOH) 4.54 71.3 0.60.81  74 10(LiOH) 3.38 52.5 4.2 0.818 72 11(LiOH) 2.34 35.9 18.6 0.81572 12(KOH) 5.3 36 19.3 Broke 70 13(KOH) 8.26 57.9 7.18 0.804 70 14(KOH)l0.7 77 4.3 0.801 67 15(ZnAc) 17.9 71.5 0.2 0.806 71 16(ZnAc) 13.9 530.9 0.797 69 17(ZnAc) 9.91 36.1 3.4 0.793 67 18(MgAc) 17.4 70.7 2.80.814 74 19(MgAc) 20.6 87.1 1.5 0.815 76 20(MgAc) 13.8 53.8 4.1 0.814 7421(CaAc) 13.2 69.2 1.1 0.813 74 22(CaAc) 7.12 34.9 10.1 0.808 70 23(MgO)2.91 53.5 2.5 0.813 24(MgO) 3.85 71.5 2.8 0.808 25(MgO) 4.76 89.3 1.10.809 26(MgO) 1.96 35.7 7.5 0.815 27(NiAC) 13.04 61.1 0.2 0.802 7128(NiAc) 10.71 48.9 0.5 0.799 72 29(NiAC) 8.26 36.7 1.8 0.796 6930(NiAC) 5.66 24.4 7.5 0.786 64 Controls: 50/50 Blend of Ioteks8000/7030 C.O.R. = .810/65 Shore D Hardness DuPont High Acid Surlyn ®8422 (Na) C.O.R. = .811/70 Shore D Hardness DuPont High Acid Surlyn ®8162 (Zn) C.O.R. = .807/65 Shore D Hardness Exxon High Acid Iotek Ex-960(Zn) C.O.R. = .796/65 Shore D Hardness Control for Formulations 23-26 is50/50 Iotek 8000/7030, C.O.R. = .814, Formulatin 26 C.O.R. wasnormalized to that control accordingly Control for Formulation Nos.27-30 is 50/50 Iotek 8000/7030, C.O.R. = .807

When compared to low acid versions of similar cation neutralized ionomerresins, the new metal cation neutralized high acid ionomer resinsexhibit enhanced hardness, modulus and resilience characteristics. Theseare properties that are particularly desirable in a number ofthermoplastic fields, including the field of golf ball manufacturing.

When utilized in the construction of the inner layer of a multi-layeredgolf ball, it has been found that the new acrylic acid based high acidionomers extend the range of hardness beyond that previously obtainablewhile maintaining the beneficial properties (i.e. durability, click,feel, etc.) of the softer low acid ionomer covered balls, such as ballsproduced utilizing the low acid ionomers disclosed in U.S. Pat. Nos.4,884,814 and 4,911,451.

Moreover, as a result of the development of a number of new acrylic acidbased high acid ionomer resins neutralized to various extents by severaldifferent types of metal cations, such as manganese, lithium, potassium,calcium and nickel cations, several new ionomers or ionomer blends arenow available for production of an inner cover layer of a multi-layeredgolf ball. By using these high acid ionomer resins, harder, stifferinner cover layers having higher C.O.R.s, and thus longer distance, canbe obtained.

More preferably, it has been found that when two or more of theabove-indicated high acid ionomers, particularly blends of sodium andzinc high acid ionomers, are processed to produce the covers ofmulti-layered golf balls, (i.e., the inner cover layer herein) theresulting golf balls will travel further than previously knownmulti-layered golf balls produced with low acid ionomer resin covers dueto the balls' enhanced coefficient of restitution values.

The low acid ionomers which may be suitable for use in formulating theinner layer compositions of several of the embodiments of the subjectinvention are ionic copolymers which are the metal, i.e., sodium, zinc,magnesium, etc., salts of the reaction product of an olefin having fromabout 2 to 8 carbon atoms and an unsaturated monocarboxylic acid havingfrom about 3 to 8 carbon atoms. Preferably, the ionomeric resins arecopolymers of ethylene and either acrylic or methacrylic acid. In somecircumstances, an additional comonomer such as an acrylate ester (i.e.,iso- or n-butylacrylate, etc.) can also be included to produce a softerterpolymer. The carboxylic acid groups of the copolymer are neutralizedor partially neutralized (i.e., approximately 10-100%, preferably30-70%) by the metal ions. Each of the low acid ionomer resins which maybe included in the inner layer cover compositions of the inventioncontains 16% by weight or less of a carboxylic acid.

The inner layer compositions include the low acid ionomers such as thosedeveloped and sold by E.I. DuPont de Nemours & Company under thetrademark “Surlyn®” and by Exxon Corporation under the trademark“Escor™” or tradename “Iotek,” or blends thereof.

The low acid ionomer resins available from Exxon under the designation“Escor™” and/or “Iotek,” are somewhat similar to the low acid ionomericresins available under the “Surlyn®” trademark. However, since theEscor™/Iotek ionomeric resins are sodium or zinc salts ofpoly(ethylene-acrylic acid) and the “Surlyn®” resins are zinc, sodium,magnesium, etc. salts of poly(ethylene-methacrylic acid), distinctdifferences in properties exist.

When utilized in the construction of the inner layer of a multi-layeredgolf ball, it has been found that the low acid ionomer blends extend therange of compression and spin rates beyond that previously obtainable.More preferably, it has been found that when two or more low acidionomers, particularly blends of sodium and zinc ionomers, are processedto produce the covers of multi-layered golf balls, (i.e., the innercover layer herein) the resulting golf balls will travel further and atan enhanced spin rate than previously known multi-layered golf balls.Such an improvement is particularly noticeable in enlarged or oversizedgolf balls.

The use of an inner layer formulated from blends of lower acid ionomersproduces multi-layer golf balls having enhanced compression and spinrates. These are the properties desired by the more skilled golfer.

In yet another embodiment of the inner cover layer, a blend of high andlow acid ionomer resins is used. These can be the ionomer resinsdescribed above, combined in a weight ratio which preferably is withinthe range of 10:90 to 90:10 parts of high and low acid ionomer resins.

A further additional embodiment of the inner cover layer is primarilybased upon the use of a fully non-ionomeric thermoplastic material.Suitable non-ionomeric materials include metallocene catalyzedpolyolefins or polyamides, polyamide/ionomer blends, polyphenyleneether/ionomer blends, etc., which have a shore D hardness of ≧60 and aflex modulus of greater than about 30,000 psi, or other hardness andflex modulus values which are comparable to the properties of theionomers described above. Other suitable materials include but are notlimited to thermoplastic or thermosetting polyurethanes, a polyesterelastomer such as that marketed by DuPont under the trademarkHytrel™(polyether ester), or a polyether amide such as that marketed byElf Atochem S.A. under the trademark Pebax®, a blend of two or morenon-ionomeric thermoplastic elastomers, or a blend of one or moreionomers and one or more non-ionomeric thermoplastic elastomers.

ii. Outer Cover Layer

While the dual core component described below, and the hard inner coverlayer formed thereon, provide the multi-layer golf ball with power anddistance, the outer cover layer 16 is comparatively softer than theinner cover layer. The softness provides for the feel and playabilitycharacteristics typically associated with balata or balata-blend balls.The outer cover layer or ply is comprised of a relatively soft, lowmodulus (about 1,000 psi to about 10,100 psi) and, in an alternateembodiment, low acid (less than 16 weight percent acid) ionomer, anionomer blend, a non-ionomeric thermoplastic or thermosetting materialsuch as, but not limited to, a metallocene catalyzed polyolefin such asEXACT™ material available from EXXON®, a polyurethane, a polyesterelastomer such as that marketed by DuPont under the trademark Hytrel™,or a polyether amide such as that marketed by Elf Atochem S.A. under thetrademark Pebax®, a blend of two or more non-ionomeric thermoplastic orthermosetting materials, or a blend of one or more ionomers and one ormore non-ionomeric thermoplastic materials.

The outer layer is fairly thin (i.e. from about 0.010 to about 0.10inches in thickness, more desirably 0.03 to 0.06 inches in thickness fora 1.680 inch ball and 0.03 to 0.06 inches in thickness for a 1.72 inchor more ball), but thick enough to achieve desired playabilitycharacteristics while minimizing expense. Thickness is defined as theaverage thickness of the non-dimpled areas of the outer cover layer. Theouter cover layer, such as layer 16, has a Shore D hardness of at least1 point softer than the inner cover or Shore D of 57 or less.

In one embodiment, the outer cover layer preferably is formed from anionomer which constitutes at least 75 weight % of an acrylateester-containing ionic copolymer or blend of acrylate ester-containingionic copolymers. This type of outer cover layer in combination with thecore and inner cover layer described above results in golf ball covershaving a favorable combination of durability and spin rate. The one ormore acrylate ester-containing ionic copolymers each contain an olefin,an acrylate ester, and an acid. In a blend of two or more acrylateester-containing ionic copolymers, each copolymer may contain the sameor a different olefin, acrylate ester and acid than are contained in theother copolymers. Preferably, the acrylate ester-containing ioniccopolymer or copolymers are terpolymers, but additional monomers can becombined into the copolymers if the monomers do not substantially reducethe scuff resistance or other good playability properties of the cover.

For a given copolymer, the olefin is selected from the group consistingof olefins having 2 to 8 carbon atoms, including, as non-limitingexamples, ethylene, propylene, butene-1, hexene-1 and the like.Preferably the olefin is ethylene.

The acrylate ester is an unsaturated monomer having from 1 to 21 carbonatoms which serves as a softening comonomer. The acrylate esterpreferably is methyl, ethyl, n-propyl, n-butyl, n-octyl, 2-ethylhexyl,or 2-methoxyethyl 1-acrylate, and most preferably is methyl acrylate orn-butyl acrylate. Another suitable type of softening comonomer is analkyl vinyl ether selected from the group consisting of n-butyl,n-hexyl, 2-ethylhexyl, and 2-methoxyethyl vinyl ethers.

The acid is a mono- or dicarboxylic acid and preferably is selected fromthe group consisting of methacrylic, acrylic, ethacrylic,α-chloroacrylic, crotonic, maleic, fumaric, and itaconic acid, or thelike, and half esters of maleic, fumaric and itaconic acid, or the like.The acid group of the copolymer is 10-100% neutralized with any suitablecation, for example, zinc, sodium, magnesium, lithium, potassium,calcium, manganese, nickel, chromium, tin, aluminum, or the like. It hasbeen found that particularly good results are obtained when theneutralization level is about 50-100%.

The one or more acrylate ester-containing ionic copolymers each has anindividual Shore D hardness of about 5-64. The overall Shore D hardnessof the outer cover is 57 or less, and generally is 40-55. It ispreferred that the overall Shore D hardness of the outer cover is in therange of 40-50 in order to impart particularly good playabilitycharacteristics to the ball.

The outer cover layer of the invention is formed over a core to resultin a golf ball having a coefficient of restitution of at least 0.760,more preferably at least 0.770, and most preferably at least 0.780. Thecoefficient of restitution of the ball will depend upon the propertiesof both the core and the cover. The PGA compression of the golf ball is100 or less, and preferably is 90 or less.

The acrylate ester-containing ionic copolymer or copolymers used in theouter cover layer can be obtained by neutralizing commercially availableacrylate ester-containing acid copolymers such as polyethylene-methylacrylate-acrylic acid terpolymers, including ESCOR™ ATX (Exxon ChemicalCompany) or poly (ethylene-butyl acrylate-methacrylic acid) terpolymers,including NUCREL® (DuPont Chemical Company). Particularly preferredcommercially available materials include ATX 320, ATX 325, ATX 310, ATX350, and blends of these materials with NUCREL® 010 and NUCREL® 035. Theacid groups of these materials and blends are neutralized with one ormore of various cation salts including zinc, sodium, magnesium, lithium,potassium, calcium, manganese, nickel, etc. The degree of neutralizationranges from 10-100%. Generally, a higher degree of neutralizationresults in a harder and tougher cover material. The properties ofnon-limiting examples of commercially available un-neutralized acidterpolymers which can be used to form the golf ball outer cover layersof the invention are provided below in Table 7.

TABLE 7 Properties of Un-Neutralized Acid Terpolymers Flex Melt IndexModulus dg/min Acid No. MPa Hardness Trade Name ASTM D 1238 % KOH/g(ASTM D790) (Shore D) ATX 310 6 45 80 44 ATX 320 5 45 50 34 ATX 325 2045 9 30 ATX 350 6 15 20 28 Nucrel ® 010 11 60 40 40 Nucrel ® 035 35 6059 40

The ionomer resins used to form the outer cover layers can be producedby reacting the acrylate ester-containing acid copolymer with variousamounts of the metal cation salts at a temperature above the crystallinemelting point of the copolymer, such as a temperature from about 200° F.to about 500° F., preferably from about 250° F. to about 350° F., underhigh shear conditions at a pressure of from about 100 psi to 10,000 psi.Other well known blending techniques may also be used. The amount ofmetal cation salt utilized to produce the neutralized ionic copolymersis the quantity which provides a sufficient amount of the metal cationsto neutralize the desired percentage of the carboxylic acid groups inthe high acid copolymer. When two or more different copolymers are to beused, the copolymers can be blended before or after neutralization.Generally, it is preferable to blend the copolymers before they areneutralized to provide for optimal mixing.

The compatibility of the acrylate ester-containing copolymers with eachother in a copolymer blend produces a golf ball outer cover layer havinga surprisingly good scuff resistance for a given hardness of the outercover layer. The golf ball according to the invention has a scuffresistance of no higher than 3.0. It is preferred that the golf ball hasa scuff resistance of no higher than about 2.5 to ensure that the golfball is scuff resistant when used in conjunction with a variety of typesof clubs, including sharp-grooved irons, which are particularly inclinedto result in scuffing of golf ball covers. The best results according tothe invention are obtained when the outer cover layer has a scuffresistance of no more than about 2.0.

Additional materials may also be added to the inner and outer coverlayer of the present invention as long as they do not substantiallyreduce the playability properties of the ball. Such materials includedyes (for example, Ultramarine Blue™ sold by Whitaker, Clark, andDaniels of South Plainsfield, N.J.) (see U.S. Pat. No. 4,679,795),pigments such as titanium dioxide, zinc oxide, barium sulfate and zincsulfate; UV absorbers; optical brighteners such as Eastobrite™ OB-1 andUvitex™ OB antioxidants; antistatic agents; and stabilizers. Moreover,the cover compositions of the present invention may also containsoftening agents such as those disclosed in U.S. Pat. Nos. 5,312,857 and5,306,760, including plasticizers, metal stearates, processing acids,etc., and reinforcing materials such as glass fibers and inorganicfillers, as long as the desired properties produced by the golf ballcovers of the invention are not impaired.

The outer layer in another embodiment of the invention includes a blendof a soft (low acid) ionomer resin with a small amount of a hard (highacid) ionomer resin. A low modulus ionomer suitable for use in the outerlayer blend has a flexural modulus measuring from about 1,000 to about10,000 psi, with a hardness of about 20 to about 40 on the Shore Dscale. A high modulus ionomer herein is one which measures from about15,000 to about 70,000 psi as measured in accordance with ASTM methodD-790. The hardness may be defined as at least 50 on the Shore D scaleas measured in accordance with ASTM method D-2240, but on the ball andnot on a plaque.

Soft ionomers primarily are used in formulating the hard/soft blends ofthe cover compositions. These ionomers include acrylic acid andmethacrylic acid based soft ionomers. They are generally characterizedas comprising sodium, zinc, or other mono- or divalent metal cationsalts of a terpolymer of an olefin having from about 2 to 8 carbonatoms, methacrylic acid, acrylic acid, or another, α, β-unsaturatedcarboxylic acid, and an unsaturated monomer of the acrylate ester classhaving from 1 to 21 carbon atoms. The soft ionomer is preferably madefrom an acrylic acid base polymer is an unsaturated monomer of theacrylate ester class.

Certain ethylene-acrylic acid based soft ionomer resins developed by theExxon Corporation under the designation “Iotek 7520” (referred toexperimentally by differences in neutralization and melt indexes as LDX195, LDX 196, LDX 218 and LDX 219) may be combined with known hardionomers such as those indicated above to produce the inner and outercover layers. The combination produces higher C.O.R.s at equal or softerhardness, higher melt flow, (which corresponds to improved, moreefficient molding, i.e., fewer rejects) as well as significant costsavings versus the outer layer of multi-layer balls produced by otherknown hard-soft ionomer blends as a result of the lower overall rawmaterials cost and improved yields.

While the exact chemical composition of the resins to be sold by Exxonunder the designation Iotek 7520 is considered by Exxon to beconfidential and proprietary information, Exxon's experimental productdata sheet lists the following physical properties of the ethyleneacrylic acid zinc ionomer developed by Exxon:

TABLE 8 Property Value ASTM Method Units Typical Physical Properties ofIotek 7520 Melt Index D-1238 g/10 min. 2 Density D-1505 kg/m³ 0.962Cation Zinc Melting Point D-3417 ° C. 66 Crystallization D-3417 ° C. 49Point Vicat Softening D-1525 ° C. 42 Point Plaque Properties (2 mm thickCompression Molded Plaques) Tensile at Break D-638 MPa 10 Yield PointD-638 MPa None Elongation at Break D-638 % 760 1% Secant Modulus D-638MPa 22 Shore D Hardness D-2240 32 Flexural Modulus D-790 MPa 26 ZwickRebound ISO 4862 % 52 De Mattia Flex D-430 Cycles >5000 Resistance

In addition, test data collected by the inventor indicates that Iotek7520 resins have Shore D hardnesses of about 32 to 36 (per ASTM D-2240),melt flow indexes of 3±0.5 g/10 min (at 190° C. per ASTM D-1288), and aflexural modulus of about 2500-3500 psi (per ASTM D-790). Furthermore,testing by an independent testing laboratory by pyrolysis massspectrometry indicates at Iotek 7520 resins are generally zinc salts ofa terpolymer of ethylene, acrylic acid, and methyl acrylate.

Furthermore, the inventor has found that a newly developed grade of anacrylic acid based soft ionomer available from the Exxon Corporationunder the designation Iotek 7510 is also effective when combined withthe hard ionomers indicated above in producing golf ball coversexhibiting higher C.O.R. values at equal or softer hardness than thoseproduced by known hard-soft ionomer blends. In this regard, Iotek 7510has the advantages (i.e. improved flow, higher C.O.R. values at equalhardness, increased clarity, etc.) produced by the Iotek 7520 resin whencompared to the methacrylic acid base soft ionomers known in the art(such as the Surlyn® 8625 and Surlyn® 8629 combinations disclosed inU.S. Pat. No. 4,884,814).

In addition, Iotek 7510, when compared to Iotek 7520, produces slightlyhigher C.O.R. values at equal softness/hardness due to the Iotek 7510'shigher hardness and neutralization. Similarly, Iotek 7510 producesbetter release properties (from the mold cavities) due to its slightlyhigher stiffness and lower flow rate than Iotek 7520. This is importantin production where the soft covered balls tend to have lower yieldscaused by sticking in the molds and subsequent punched pin marks fromthe knockouts.

According to Exxon, Iotek 7510 is of similar chemical composition asIotek 7520 (i.e. a zinc salt of a terpolymer of ethylene, acrylic acid,and methyl acrylate) but is more highly neutralized. Based upon FTIRanalysis, Iotek 7520 is estimated to be about 30-40 wt.-% neutralizedand Iotek 7510 is estimated to be about 40-60 wt.-% neutralized. Thetypical properties of Iotek 7510 in comparison of those of Iotek 7520 incomparison of those of Iotek 7520 are set forth below:

TABLE 9 Physical Properties of Iotek 7510 in Comparison to Iotek 7520IOTEK 7520 IOTEK 7510 MI, g/10 min 2.0 0.8 Density, g/cc 0.96 0.97Melting Point, ° F. 151 149 Vicat Softening Point, ° F. 108 109 FlexModulus, psi 3800 5300 Tensile Strength, psi 1450 1750 Elongation, % 760690 Hardness, Shore D 32 35

The hard ionomer resins utilized to produce the outer cover layercomposition hard/soft blends include ionic copolymers which are thesodium, zinc, magnesium, lithium, etc. salts of the reaction product ofan olefin having from 2 to 8 carbon atoms and an unsaturatedmonocarboxylic acid having from 3 to 8 carbon atoms. The carboxylic acidgroups of the copolymer may be totally or partially (i.e. approximately15-75 percent) neutralized.

The hard ionomeric resins are likely copolymers of ethylene and acrylicand/or methacrylic acid, with copolymers of ethylene and acrylic acidbeing the most preferred. Two or more types of hard ionomeric resins maybe blended into the outer cover layer compositions in order to producethe desired properties of the resulting golf balls.

As discussed earlier herein, the hard ionomeric resins introduced underthe designation EscorT and sold under the designation “Iotek” aresomewhat similar to the hard ionomeric resins sold under the Surlyn®trademark. However, since the “Iotek” ionomeric resins are sodium orzinc salts of poly(ethylene-acrylic acid) and the Surlyn® resins arezinc or sodium salts of poly(ethylene-methacrylic acid) some distinctdifferences in properties exist. As more specifically indicated in thedata set forth below, the hard “Iotek” resins (i.e., the acrylic acidbased hard ionomer resins) are the more preferred hard resins for use informulating the outer layer blends for use in the present invention. Inaddition, various blends of “Iotek” and Surlyn® hard ionomeric resins,as well as other available ionomeric resins, may be utilized in thepresent invention in a similar manner.

Examples of commercially available hard ionomeric resins which may beused in the present invention in formulating the outer cover blendsinclude the hard sodium ionic copolymer sold under the trademark Surlyn®8940 and the hard zinc ionic copolymer sold under the trademark Surlyn®9910. Surlyn® 8940 is a copolymer of ethylene with methacrylic acid andabout 15 weight percent acid which is about 29 percent neutralized withsodium ions. This resin has an average melt flow index of about 2.8.Surlyn® 9910 is a copolymer of ethylene and methacrylic acid with about15 weight percent acid which is about 58 percent neutralized with zincions. The average melt flow index of Surlyn® 9910 is about 0.7. Thetypical properties of Surlyn® 9910 and 8940 are set forth below in Table10:

TABLE 10 Typical Properties of Commercially Available Hard Surlyn ®Resins Suitable for Use in the Outer Layer Blends of the PresentInvention ASTM D 8940 9910 8920 8528 9970 9730 Cation Type Sodium ZincSodium Sodium Zinc Zinc Melt flow index, gms/10 min. D-1238 2.8 0.7 0.91.3 14.0 1.6 Specific Gravity, g/cm³ D-792 0.95 0.97 0.95 0.94 0.95 0.95Hardness, Shore D D-2240 66 64 66 60 62 63 Tensile Strength, (kpsi) MPaD-636  (4.8)  (3.6)  (5.4)  (4.2)  (3.2)  (4.1) 33.1 24.8 37.2 29.0 22.028.0 Elongation, % D-638 470 290 350 450 460 460 Flexural Modulus,(kpsi) MPa D-790  (51)  (48)  (55)  (32)  (28)  (30) 350 330 380 220 190210 Tensile Impact (23° C.) D-1822S 1020 1020 865 1160 760 1240 KJ/m₂(ft.-lbs./in²) (485) (485) (410) (550) (360) (590) Vicat Temperature, °C. D-1525 63 62 58 73 61 73

Examples of the more pertinent acrylic acid based hard ionomer resinsuitable for use in the present outer cover composition sold under the“Iotek” trade name by the Exxon Corporation include Iotek 8000, 8010,8020, 8030, 7030, 7010, 7020, 1002, 1003, 959 and 960. The physicalproperties of Iotek 959 and 960 are shown above. The typical propertiesof the remainder of these and other Iotek hard ionomers suited for usein formulating the outer layer cover composition are set forth below inTable 11:

TABLE 11 Typical Properties of Iotek Ionomers ASTM Method Units 40004010 8000 8020 8030 Resin Properties Cation type zinc zinc sodium sodiumsodium Melt index D-1238 g/10 min. 2.5 1.5 0.8 1.6 2.8 Density D-1505kg/m³ 963 963 954 960 960 Melting Point D-3417 ° C. 90 90 90 87.5 87.5Crystallization Point D-3417 ° C. 62 64 56 53 55 Vicat Softening PointD-1525 ° C. 62 63 61 64 67 % Weight Acrylic Acid 16 15 % of Acid Groups30 40 cation neutralized Plaque Properties (3 mm thick, compressionmolded) Tensile at break D-638 MPa 24 26 36 31.5 28 Yield point D-638MPa none none 21 21 23 Elongation at break D-638 % 395 420 350 410 3951% Secant modulus D-638 MPa 160 160 300 350 390 Shore Hardness D D-2240— 55 55 61 58 59 Film Properties (50 micron film 2.2:1 Blow-up ratio)Tensile at Break MD D-882 MPa 41 39 42 52 47.4 TD D-882 MPa 37 38 38 3840.5 Yield point MD D-882 MPa 15 17 17 23 21.6 TD D-882 MPa 14 15 15 2120.7 Elongation at Break MD D-882 % 310 270 260 295 305 TD D-882 % 360340 280 340 345 1% Secant modulus MD D-882 MPa 210 215 390 380 380 TDD-882 MPa 200 225 380 350 345 Dart Drop Impact D-1709 g/micron 12.4 12.520.3 7010 7020 7030 Resin Properties Cation type zinc zinc zinc MeltIndex D-1238 g/10 min. 0.8 1.5 2.5 Density D-1505 kg/m³ 960 960 960Melting Point D-3417 ° C. 90 90 90 Crystallization Point D-3417 ° C. — —— Vicat Softening Point D-1525 ° C. 60 63 62.5 % Weight Acrylic Acid %of Acid Groups Cation Neutralized Plaque Properties (3 mm thickcompression molded) Tensile at break D-638 MPa 38 38 38 Yield PointD-638 MPa none none none Elongation at break D-638 % 500 420 395 1%Secant modulus D-638 MPa — — — Shore Hardness D D-240 — 57 55 55

It has been determined that when hard/soft ionomer blends are used forthe outer cover layer, good results are achieved when the relativecombination is in a range of about 3-25 percent hard ionomer and about75-97 percent soft ionomer.

Moreover, in alternative embodiments, the outer cover layer formulationmay also comprise up to 100 wt % of a soft, low modulus non-ionomericthermoplastic material including a polyester polyurethane such as B.F.Goodrich Company's Estane® polyester polyurethane X4517. Thenon-ionomeric thermoplastic material may be blended with a soft ionomer.For example, polyamides blend well with soft ionomer. According to B.F.Goodrich, Estane® X-4517 has the following properties:

Properties of Estane ® X-4517 Tensile 1430 100%  815 200% 1024 300% 1193Elongation  641 Youngs Modulus 1826 Hardness A/D 88/39 Bayshore Rebound 59 Solubility in Water Insoluble Melt processing temperature >350° F.(>177° C.) Specific Gravity (H₂O = 1) 1.1-1.3

Other soft, relatively low modulus non-ionomeric thermoplasticelastomers may also be utilized to produce the outer cover layer as longas the non-ionomeric thermoplastic elastomers produce the playabilityand durability characteristics desired without adversely effecting theenhanced travel distance characteristic produced by the high acidionomer resin composition. These include, but are not limited to,thermoplastic polyurethanes such as Texin™, thermoplastic polyurethanesfrom Mobay Chemical Co. and the Pellethane™ thermoplastic polyurethanesfrom Dow Chemical Co.; non-ionomeric thermoset polyurethanes includingbut not limited to those disclosed in U.S. Pat. No. 5,334,673;cross-linked metallocene catalyzed polyolefins; ionomer/rubber blendssuch as those in Applicants' U.S. Pat. Nos. 4,986,545; 5,098,105 and5,187,013; and, Hytrel™ polyester elastomers from DuPont and Pebax®polyetheramides from Elf Atochem S.A.

B. Single Layer Covers

The cores of the present invention can also be covered by a single coverlayer. Preferably, the single layer covers are comprised of the outerlayer cover materials discussed above. Additionally, the single layercovers can also comprise the inner cover materials referenced above.

Method of Making Golf Ball

In preparing golf balls in accordance with the present invention, acover layer is molded (by injection molding or by compression molding)about a core (a dual core).

The dual cores of the present invention are preferably formed by thecompression molding techniques set forth above. However, it is fullycontemplated that liquid injection molding or transfer moldingtechniques could also be utilized.

A relatively hard inner cover layer is then molded about the resultingdual core component. The diameter of the inner cover is about 1.570inches. A comparatively softer outer cover layer is then molded aboutthe inner cover layer. The outer cover diameter is about 1.680 inches.Details of molding the inner and outer covers are set forth herein.Alternatively, a single soft cover can be molded around the dual core.

Generally, the inner cover layer which is molded over the dual corecomponent, is about 0.01 inches to about 0.10 inches in thickness,preferably about 0.03-0.07 inches thick. The inner ball which includesthe core and inner cover layer preferably has a diameter in the range of1.25 to 1.60 inches. The outer cover layer is about 0.01 inches to about0.10 inches in thickness. Together, the dual core, the inner cover layerand the outer cover layer combine to form a ball having a diameter of1.680 inches or more, the minimum diameter permitted by the rules of theUnited States Golf Association and weighing no more than 1.62 ounces.

Most preferably, the resulting golf balls in accordance with the presentinvention have the following dimensions:

Size Specifications: Range Preferred Inner Core - Max. 0.830″ 0.344″ -Min. 0.200″ 0.340″ Outer Core - Max. 1.60″  1.595″ - Min. 1.25″  1.47″ Cover Thickness - Max. 0.215″ 0.065″ - Min. 0.040″ 0.040″

In a particularly preferred embodiment of the invention, the golf ballhas a dimple pattern which provides coverage of 60%-70% or more. Thegolf ball typically is coated with a durable, abrasion-resistant,relatively non-yellowing finish coat.

The various cover composition layers of the present invention may beproduced according to conventional melt blending procedures. Generally,the copolymer resins are blended in a Banbury™ type mixer, two-rollmill, or extruder prior to neutralization. After blending,neutralization then occurs in the melt or molten states in the Banbury™mixer. Mixing problems are minimal because preferably more than 75 wt %,and more preferably at least 80 wt % of the ionic copolymers in themixture contain acrylate esters and, in this respect, most of thepolymer chains in the mixture are similar to each other. The blendedcomposition is then formed into slabs, pellets, etc., and maintained insuch a state until molding is desired.

Alternatively, a simple dry blend of the pelletized or granulated resinswhich have previously been neutralized to a desired extent and coloredmasterbatch may be prepared and fed directly into the injection moldingmachine where homogenization occurs in the mixing section of the barrelprior to injection into the mold. If necessary, further additives suchas an inorganic filler, etc., may be added and uniformly mixed beforeinitiation of the molding process. A similar process is utilized toformulate the high acid ionomer resin compositions used to produce theinner cover layer. In one embodiment of the invention, a masterbatch ofnon-acrylate ester-containing ionomer with pigments and other additivesincorporated therein is mixed with the acrylate ester-containingcopolymers in a ratio of about 1-7 weight % masterbatch and 93-99 weight% acrylate ester-containing copolymer. However, a masterbatch isgenerally not used commercially to form the inner cover or mantle layerdue to cost concerns.

The golf balls of the present invention can also be produced by moldingprocesses which include but are not limited to those which are currentlywell known in the golf ball art. For example, the golf balls can beproduced by injection molding or compression molding the novel covercompositions around a solid molded core to produce an inner ball whichtypically has a diameter of about 1.25 to 1.60 inches. The core,preferably of a dual core configuration, may be formed as previouslydescribed. The outer layer is subsequently molded over the inner layerto produce a golf ball having a diameter of preferably about 1.680inches or more.

In compression molding, the inner cover composition is formed viainjection at about 380° F. to about 450° F. into smooth surfacedhemispherical shells which are then positioned around the core in a moldhaving the desired inner cover thickness and subjected to compressionmolding at 200° to 300° F. for about 2 to 10 minutes, followed bycooling at 50° to 70° F. for about 2 to 7 minutes to fuse the shellstogether to form a unitary intermediate ball. In addition, theintermediate balls may be produced by injection molding wherein theinner cover layer is injected directly around the core placed at thecenter of an intermediate ball mold for a period of time in a moldtemperature of from 50° to about 100° F. Subsequently, the outer coverlayer is molded around the core and the inner layer by similarcompression or injection molding techniques to form a dimpled golf ballof a diameter of 1.680 inches or more.

After formation of the balls, the balls are optionally subjected togamma radiation. This has been found to crosslink the cover to improvescuff and cut resistance. Furthermore, the gamma radiation has also beenfound to increase the crosslink density of the core and results in aharder and higher compression core and ball. And so, the Shore Chardness of the core typically increases after gamma treatment.

After molding and/or radiation treatment, the golf balls produced mayundergo various further processing steps such as buffing, painting andmarking as disclosed in U.S. Pat. No. 4,911,451.

The resulting golf ball produced from the hard inner layer and therelatively softer, low flexural modulus outer layer provide for animproved multi-layer golf ball having a unique dual core configurationwhich provides for desirable coefficient of restitution and durabilityproperties while at the same time offering the feel and spincharacteristics associated with soft balata and balata-like covers ofthe prior art.

Golf balls according to the invention preferably have a PGA compressionof 10-120. In a particularly preferred form of the invention, the golfballs have a PGA compression of about 40-100. It has been found thatexcellent results are obtained when the PGA compression of the golfballs is 60-100. The coefficient of restitution of the golf balls of theinvention is in the range of 0.770 or greater. Preferably, the C.O.R. ofthe golf balls is in the range of 0.770-0.830 and most preferably0.790-0.830.

As mentioned above, resiliency and compression are amongst the principalproperties involved in a golf ball's performance. In the past, PGAcompression related to a scale of 0 to 200 given to a golf ball. Thelower the PGA compression value, the softer the feel of the ball uponstriking. In practice, tournament quality balls have compression ratingsaround 70-110, preferably around 80 to 100.

In determining PGA compression using the 0-200 scale, a standard forceis applied to the external surface of the ball. A ball which exhibits nodeflection (0.0 inches in deflection) is rated 200 and a ball whichdeflects {fraction (2/10)}th of an inch (0.2 inches) is rated 0. Everychange of 0.001 of an inch in deflection represents a 1 point drop incompression. Consequently, a ball which deflects 0.1 inches (100×0.001inches) has a PGA compression value of 100 (i.e., 200-100) and a ballwhich deflects 0.110 inches (110×0.001 inches) has a PGA compression of90 (i.e., 200-110).

In order to assist in the determination of compression, several deviceshave been employed by the industry. For example, PGA compression indetermined by an apparatus fashioned in the form of a small press withan upper and lower anvil. The upper anvil is at rest against a diespring, and the lower anvil is movable through 0.300 inches by means ofa crank mechanism. In its open position the gap between the anvils is1.780 inches allowing a clearance of 0.100 inches for insertion of theball. As the lower anvil is raised by the crank, it compresses the ballagainst the upper anvil, such compression occurring during the last0.200 inches of stroke of the lower anvil, the ball then loading theupper anvil which in turn loads the spring. The equilibrium point of theupper anvil is measured by a dial micrometer if the anvil is deflectedby the ball more than 0.100 inches (less deflection is simply regardedas zero compression) and the reading on the micrometer dial is referredto as the compression of the ball. In practice, tournament quality ballshave compression ratings around 80 to 100 which means that the upperanvil was deflected a total of 0.120 to 0.100 inches.

An example to determine PGA compression can be shown by utilizing a golfball compression tester produced by Atti Engineering Corporation ofNewark, N.J., now manufactured by OK Automation of Sinking Spring, Pa.The value obtained by this tester relates to an arbitrary valueexpressed by a number which may range from 0 to 100, although a value of200 can be measured as indicated by two revolutions of the dialindicator on the apparatus. The value obtained defines the deflectionthat a golf ball undergoes when subjected to compressive loading. TheAtti test apparatus consists of a lower movable platform and an uppermovable spring-loaded anvil. The dial indicator is mounted such that itmeasures the upward movement of the spring loaded anvil. The golf ballto be tested is placed in the lower platform, which is then raised afixed distance. The upper portion of the golf ball comes in contact withand exerts a pressure on the springloaded anvil. Depending upon thedistance of the golf ball to be compressed, the upper anvil is forcedupward against the spring.

Alternative devices have also been employed to determine compression.For example, Applicants also utilize a modified Riehle CompressionMachine originally produced by Riehle Bros. Testing Machine Company,Phil., Pa. to evaluate compression of the various components (i.e.,cores, mantle cover balls, finished balls, etc.) of the golf balls. TheRiehle compression device determines deformation in thousandths of aninch under a load designed to emulate the force applied by the Atti orPGA compression tester. Using such a device, a Riehle compression of 61corresponds to a deflection under load of 0.061 inches.

Additionally, an approximate relationship between Riehle compression andPGA compression exists for balls of the same size. It has beendetermined by Applicants that Riehle compression corresponds to PGAcompression by the general formula PGA compression=160−Riehlecompression. Consequently, 80 Riehle compression corresponds to 80 PGAcompression, 70 Riehle corresponds to 90 PGA compression, and 60 PGAcompression corresponds to 100 PGA compression. For reporting purposes,Applicants' compression values are usually measured as Riehlecompression and converted to PGA compression.

Furthermore, additional compression devices may also be utilized tomonitor golf ball compression so long as the correlation to PGAcompression is known. These devices have been designed, such as aWhitney Tester, to correlate or correspond to PGA compression through aset relationship or formula.

As used herein, “Shore D hardness” or “Shore C hardness” of a core orcover component is measured generally in accordance with ASTM D-2240,except the measurements are made on the curved surface of the moldedcomponent, rather than on a plaque. Furthermore, the Shore C-D hardnessof the cover is measured while the cover remains over the core. When ahardness measurement is made on a dimpled cover, Shore C-D hardness ismeasured at a land area of the dimpled cover.

Golf balls according to the invention have a cut resistance in the rangeof 1-3 on a scale of 1-5. It is preferred that the golf balls of theinvention have a cut resistance of 1-2.5 and most preferably 1-2.

The scuff resistance test was conducted in the following manner: aTop-Flite® Tour pitching wedge (1994) with box grooves was obtained andwas mounted in a Miyamae™ driving machine. The club face was orientedfor a square hit. The forward/backward tee position was adjusted so thatthe tee was four inches behind the point in the downswing where the clubwas vertical. The height of the tee and the toe-heel position of theclub relative to the tee were adjusted in order that the center of theimpact mark was about ¾ of an inch above the sole and was centered toeto heel across the face. The machine was operated at a clubhead speed of125 feet per second. Three samples of each ball were tested. Each ballwas hit three times. After testing, the balls were rated according tothe following table:

Rating Type of damage 1 Little or no damage (groove markings or dents) 2Small cuts and/or ripples in cover 3 Moderate amount of material liftedfrom ball surface but still attached to ball 4 Material removed orbarely attached

Cut resistance was measured in accordance with the following procedure:A golf ball was fired at 135 feet per second against the leading edge ofa 1994 Top-Flite® Tour pitching wedge, wherein the leading edge radiusis {fraction (1/32)} inch, the loft angle is 51 degrees, the sole radiusis 2.5 inches, and the bounce angle is 7 degrees. The cut resistance ofthe balls tested herein was evaluated on a scale of 1-5. A 5 representsa cut that extends completely through the cover to the Core; a 4represents a cut that does not extend completely through the cover butthat does break the surface; a 3 does not break the surface of the coverbut does leave a permanent dent; a 2 leaves only a slight crease whichis permanent but not as severe as 3; and a 1 represents virtually novisible indentation or damage of any sort.

The spin rate of the ball of the invention may be tested in the mannerdescribed in Example 2 below.

Having generally described the invention, the following examples areincluded for purposes of illustration so that the invention may be morereadily understood and are in no way intended to limit the scope of theinvention unless otherwise specifically indicated.

EXAMPLES Example 1 Dual Core Golf Ball With Heavy Elastomeric NucleusComprising a Tungsten Powder/ Polybutadiene Rubber Core, {fraction(11/32)}″ Diameter

1A. A Dual Core and a Dual Cover Golf Ball

A heavy spherical center core layer containing powdered tungsten metalin a polybutadiene matrix and having a diameter of 0.344 inches (8.74mm) was formed with the following composition:

Components phr Neo Cis 40 Butadiene Rubber 100.0 Kulite ™ TungstenPowder (5 microns) 1248.5 Iron Powder 100.0 Zinc Oxide 5.0 Varox ™ 231XLPeroxide Initiator 3.0 Zinc Diacrylate 0.0 TOTAL 1456.5

The spherical center core layer comprising the above compositionexhibited a specific gravity of 7.65, a weight of 2.7 grams, and a ShoreC hardness of 80 (preferred range is 50-95).

The iron powder of the above composition was optional and was added tothe composition in order to attract the formed center to a magnet. Suchattraction allows for automated assembly of the 0.344 inch sphericalcenter to the uncured preformed half shells in golf ball production.

As mentioned above, zinc diacrylate (ZDA) is not included in thecomposition of the center core layer of the present invention. Zincdiacrylate is normally added to core compositions in golf ballproduction in order to increase hardness.

An outer core layer was disposed about the spherical center core layerpresented above. The outer core layer had the following composition:

Components phr BCP-820 40 Neo Cis 40 30 Neo Cis 60 30 Zinc Oxide 13.7Zinc Stearate 16 Zinc Diacrylate 21.3 Trigonox 42-40 1.25 Total 152.25

The molded dual core comprising a spherical center and outer core layerwith the above compositions exhibited the following properties:

Molded Dual Core Properties Size (inches) 1.478 (37.5 mm) Weight (grams)32.83 Riehle Compression 140 (.140 inches of deformation) C.O.R.  0.768Specific Gravity  1.10

A centerless ground dual core comprising a spherical center and outercore layer with the above compositions exhibited the followingproperties:

Centerless Ground Dual Core Properties Size (inches) 1.469 (37.3 mm)Weight (grams) 32.24 Riehle Compression 137 (.137 inches) C.O.R.  0.774Specific Gravity  1.18

In forming a multi-layered golf ball comprising the dual core having aspherical center core layer and an outer core layer with the abovecompositions, the following inner cover layer, i.e., mantle layer,composition was used:

Inner Cover (Mantle) Layer Composition Components phr Iotek 1002 50Iotek 1003 50 Total 100 

Upon the formation of the inner cover layer on the dual core to form anintermediate ball, the combination of an inner cover layer and dual coreexhibited the following properties:

Combination of Inner Cover Layer and Dual Core Properties Size (inches)1.570 Weight (grams) 38.3 Riehle Compression 113 (.113 inches) C.O.R.0.803 Shore D 68-72 Specific Gravity 1.15

An outer cover layer was disposed about the inner cover layer having thefollowing formulation:

Outer Cover Layer Composition Components Parts by Weight Iotek 7510 41Iotek 7520 49.5 White M.B.¹ 9.5 ¹White M.B. comprises the followingcomposition: 100 pts. Surlyn AD8549 31.3 pts. Unitane 0-110 0.60 pts.Ultra Marine Blue 0.34 pts. Eastobrite OB-1 0.05 pts. Santonox R

The molded balls may optionally be subjected to gamma radiationtreatment at about 40 kilograys to crosslink the cover to improve scuffand cut resistance. The gamma radiation also increases the crosslinkdensity of the core and results in a harder core and ball compression.Below is a comparison of properties exhibited by a golf ball prior togamma radiation and properties exhibited by a golf ball subjected togamma radiation:

Dual Core, Multi-Layered, Golf Ball Properties Riehle Golf Ball Size(inches) Weight (grams) Compression C.O.R. Molded Ball 1.685 45.2 104 0.789 Before Gamma (.104 inches) Radiation Molded Ball 1.683 45.2 870.805 After Gamma (.087 inches) Radiation Finished Golf 1.684 45.3 870.805 Ball (.087 inches)

1B. A Dual Core and Single Layer Golf Ball

A spherical center core layer having a diameter of 0.344 inches wasformed with the following composition:

Components phr Neo Cis 40 Butadiene Rubber 100.0 Kulite Tungsten Powder(5 microns) 1248.5 Iron Powder 100.0 Zinc Oxide 5.0 Varox 231XL Peroxide3.0 Zinc Diacrylate 0.0 TOTAL 1456.5

The spherical center comprising the above composition exhibited aspecific gravity of 7.65, a weight of 2.7 grams, and a Shore C hardnessof 80.

Again, the iron powder of the above composition was again optional andwas added to the composition in order to attract the composition to amagnet. As mentioned above, such attraction allows for automatedassembly of the 0.344 inch spherical center to the uncured preformedhalf shells in golf ball production.

An outer core layer was disposed about the spherical center having thefollowing composition:

Components phr BCP-820 40 Neo Cis 40 30 Neo Cis 60 30 Zinc Oxide 9.5Zinc Stearate 16 Zinc Diacrylate 29 Trignonox 42-40 1.25 Total 155.75

The molded dual core comprising a spherical center core layer and anouter core layer with the above compositions exhibited the followingproperties:

Molded Dual Core Properties (with {fraction (11/32)}″ Heavy WeightSpherical Center) Size (inches) 1.559 Weight (grams) 38.1 RiehleCompression 94 (0.094″) C.O.R. 0.799 Specific Gravity 1.11

A single layer cover was disposed about the dual core having thefollowing composition:

Cover Layer Composition Components Parts by Weight Iotek 7510 41 Iotek7520 49.5 White M.B.¹ 9.5 Total 100 ¹White M.B. comprises the followingcomposition: 100 pts. Surlyn AD8549 31.3 pts. Unitane 0-110 0.60 pts.Ultra Marine Blue 0.34 pts. Eastobrite OB-1 0.05 pts. Santonox R

Once again, the molded balls may optionally be subjected to gammaradiation treatment at about 40 kilograys to crosslink the cover toimprove scuff and cut resistance. The gamma radiation also increases thecrosslink density of the core and results in a harder core and ballcompression. Below is a comparison of properties exhibited by a golfball prior to gamma radiation and properties exhibited by a golf ballsubjected to gamma radiation:

Dual Core, Single-Layered Golf Ball Properties Riehle Golf Ball Size(inches) Weight (grams) Compression C.O.R. Molded Ball 1.684 45.8 960.792 Before Gamma (.096 inches) Radiation Molded Ball 1.681 45.8 770.814 After Gamma (.077 inches) Radiation Finished Golf 1.682 45.9 760.816 Ball (.076 inches)

Example 2

Spin rate testing was conducted with the finished multi-layered covered,dual core golf balls (Example 1A) and single-layered cover, dual coregolf balls (Example 1B) of above Example using a driver, a 5 iron, a 9iron, and a pitching wedge. The golf ball testing machine was set up toemulate the launch conditions of an average Touring Professional Golferfor each particular club. For comparative purposes, commercial golfballs were also tested for spin rate using the same clubs.

Below are the results of the spin rate testing:

Spin Rate Data for Examples 1A (Dual Core, Dual Cover) and 1B (DualCore, Single Cover) Spin Ball Launch Rate Velocity Club Ball Type Angle(rpm) (ft./sec.) 10.5 Intimidator ® Example 1A 10.9 3806 229.5 DriverExample 1B 10.3 3072 231.1 Strata- ™ 10.7 2896 227.4 Professional 90Precept ® MC Spin 11.1 2888 226.5 Titleist ® 11.0 3074 227.7 Prestige 905 Iron Apex Plus ™ Example 1A 15.7 5798 184.5 Example 1B 15.0 7347 182.2Strata- ™ 15.8 5713 182.5 Professional 90 Precept ® MC Spin 15.8 5445183.1 Titleist ® 15.2 5840 181.3 Prestige 90 9 Iron Apex Plus ™ Example1A 24.0 8658 145.2 Example 1B 21.9 10607 143.3 Strata- ™ 24.1 8713 145.4Professional 90 Precept ® MC Spin 23.9 8579 144.7 Titleist ® 24.1 8395143.7 Prestige 90 Pitching Wedge Example 1A 29.0 10571 132.9 Apex Plus ™Example 1B 27.0 12654 133.5 Strata- ™ 27.6 10467 133.6 Professional 90Precept ® MC Spin 28.2 10656 132.5 Titleist ® 29.2 10105 130.0 Prestige90

The above results indicate that the solid, non-wound golf balls having aheavy elastomeric center exhibit enhanced overall high spin properties.

Example 3

One half of the polybutadiene rubber utilized in the inner core ofExamples 1-2 was deleted and substituted with polyisoprene.Specifically, 50 phr of Natsyn 2000 was substituted for Neo-Cis 40according to the following formula:

ACTUAL MATERIAL PHR Sp. Gr. Enichem Neo Cis 40 50.00 0.910 GoodyearNatsyn 2200 50.00 0.910 Kulite Tungsten Powder 1386.40 19.350 (5microns) Aldrich Iron Oxide, Fe₃O₄ 64.90 5.100 (less than 5 microns)Zinc Oxide 5.00 5.570 Varox 231 XL 7.50 1.410 TOTALS 1563.80 7.800

Inner cores having the following properties were produced:

size: 0.340 inches, ± 0.006 inches weight: 2.77 grams, ± 0.1 gramshardness: 62 Shore C peak ± 5 points

The inner cores, when enclosed with the above outer core and coverformulations, produced golf balls exhibiting the enhancedcharacteristics of the balls of Example 1.

The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon a reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations in so far as they come within thescope of the appended claims or the equivalents thereof.

What is claimed:
 1. A solid, non-wound, golf ball comprising: a dualcore including an inner, high density, spherical center core layer andan outer core layer disposed about said spherical center core layer,wherein said spherical center core layer has a specific gravity fromabout 2.0 to about 20.0 and a diameter of less than 0.830 inches andcomprises a blend including a powdered metal and a first matrix materialcomprising about 90 to about 10 weight percent polybutadiene and about10 to about 90 weight percent polyisoprene, wherein said blend fails tocontain a crosslinking agent comprising at least one metal salt of anunsaturated carboxylic acid and said outer core layer comprises a secondmatrix material selected from the group consisting of thermosets,thermoplastics, and combinations thereof; and an inner cover layerformed about said dual core; and an outer cover layer disposed on saidinner cover layer.
 2. A golf ball according to claim 1, wherein saidfirst matrix material of said high density spherical center core layercomprises from about 70 to about 30 weight percent polybutadiene andfrom about 30 to about 70 weight percent polyisoprene.
 3. A golf ballaccording to claim 1, wherein said first matrix material of said highdensity spherical center core layer comprises about 50 weight percentpolybutadiene and about 50 weight percent polyisoprene.
 4. A golf ballaccording to claim 1, wherein said powdered metal comprises tungstenpowder.
 5. A golf ball according to claim 1, wherein said second matrixmaterial of said outer core layer comprises polybutadiene.
 6. A golfball according to claim 1, wherein said high density spherical centercore layer has a diameter of less than 0.380 inches.
 7. A golf ballaccording to claim 1, wherein said high density spherical center corelayer has a diameter of about 0.340 inches to about 0.344 inches.
 8. Agolf ball according to claim 1, wherein said powdered metal has aspecific gravity of 2.7 or more.
 9. A golf ball according to claim 1,wherein said powdered metal has a specific gravity of 7 or more.
 10. Agolf ball according to claim 1, wherein said powdered metal is dispersedthroughout said first matrix material of said high density sphericalcenter core layer.
 11. A golf ball according to claim 10, wherein saidfirst matrix material of said high density spherical center core layeris crosslinked by the addition of peroxide.
 12. A golf ball according toclaim 10, wherein said golf ball exhibits a coefficient of restitutionof at least 0.770.
 13. A golf ball according to claim 10, wherein saidgolf ball exhibits a coefficient of restitution of at least 0.790.
 14. Agolf ball according to claim 1, wherein said golf ball exhibits a momentof inertia of less than 0.45 oz.in².
 15. A golf ball according to claim1, wherein said golf ball exhibits a moment of inertia of less than 0.44oz.in².
 16. A golf ball according to claim 1, wherein said golf ballexhibits a moment of inertia of less than 0.43 oz.in².
 17. A golf ballaccording to claim 1, wherein said golf ball is subjected to gammaradiation treatment.
 18. A golf ball according to claim 1, wherein saidpowdered metal constitutes at least 50% by weight of said sphericalcenter.
 19. A golf ball according to claim 18, wherein said powderedmetal constitutes at least 60% by weight of said spherical center.
 20. Agolf ball according to claim 18, wherein said powdered metal constitutesat least 65% by weight of said spherical center.
 21. A golf ballaccording to claim 1, wherein said powdered metal comprises a mixture oftungsten powder and iron powder.
 22. A golf ball according to claim 21,wherein said iron powder comprises 1-10% by weight of said sphericalcenter.
 23. A golf ball according to claim 1, wherein said sphericalcenter core layer has a specific gravity of about 4 to about
 18. 24. Agolf ball according to claim 1, wherein said spherical center core layerhas a specific gravity of about 5 to about
 12. 25. A golf ball accordingto claim 1, wherein said spherical center core layer has a specificgravity of about 7.6 to about 7.9.
 26. A solid, non-wound, golf ballcomprising: a dual core including an inner, high density, sphericalcenter core layer and an outer core layer disposed about said sphericalcenter core layer, wherein said spherical center core layer has aspecific gravity of 4.0 or more and comprises a blend including apowdered metal and a first matrix material comprising from about 70 toabout 30 weight percent polybutadiene and from about 30 to about 70weight percent polyisoprene; and said outer core layer comprises asecond matrix material selected from the group consisting of thermosets,thermoplastics, and combinations thereof, wherein said outer core layerhas a specific gravity of less than 1.2; and an inner cover layer formedabout said dual core; and an outer cover layer disposed on said innercover layer.
 27. A golf ball according to claim 26, wherein said firstmatrix material of said spherical center core layer comprises from about60 to about 40 weight percent polybutadiene and from about 40 to about60 weight percent polyisoprene.
 28. A golf ball according to claim 26,wherein said first matrix material of said spherical center core layercomprises about 50 weight percent polybutadiene and about 50 weightpercent polyisoprene.
 29. A golf ball according to claim 26, whereinsaid powdered metal comprises tungsten powder.
 30. A golf ball accordingto claim 26, wherein said second matrix material of said outer corelayer comprises polybutadiene.
 31. A golf ball according to claim 26,wherein said spherical center has a diameter of from about 0.200 inchesto about 0.830 inches.
 32. A golf ball according to claim 26, whereinsaid spherical center has a diameter of about 0.340 inches to about0.344 inches.
 33. A golf ball according to claim 26, wherein saidspherical center exhibits a specific gravity of greater than 7.0.
 34. Agolf ball according to claim 26, wherein said spherical center exhibitsa specific gravity of from about 4.0 to 18.0.
 35. A golf ball accordingto claim 26, wherein said powdered metal is dispersed throughout saidfirst matrix material of said spherical center.
 36. A golf ballaccording to claim 26, wherein the difference between the specificgravity of said spherical center and said outer core layer is greaterthan 2.0.
 37. A golf ball according to claim 26, wherein the differencebetween the specific gravity of said spherical center and said outercore layer is greater than 3.0.
 38. A golf ball according to claim 26,wherein said material of said spherical center is crosslinked as aresult of exposure to radiation.
 39. A golf ball according to claim 26,wherein said golf ball exhibits a moment of inertia of less than 0.45oz.in².
 40. A golf ball according to claim 26, wherein said golf ballexhibits a moment of inertia of less than 0.44 oz.in².
 41. A golf ballaccording to claim 26, wherein said golf ball exhibits a moment ofinertia of less than 0.43 oz.in².
 42. A golf ball according to claim 26,wherein said golf ball is subjected to gamma radiation treatment.
 43. Agolf ball according to claim 26, wherein said powdered metal constitutesat least 50% by weight of said spherical center.
 44. A golf ballaccording to claim 26, wherein said powdered metal constitutes at least60% by weight of said spherical center.
 45. A golf ball according toclaim 26, wherein said powdered metal constitutes at least 65% by weightof said spherical center.
 46. A golf ball according to claim 26, whereinsaid powdered metal is selected from the group consisting of tungstenpowder and iron powder and combinations thereof.
 47. A golf ballaccording to claim 46, wherein said iron powder comprises is 1-10% byweight of said spherical center.
 48. A solid, non-wound, golf ballcomprising: a dual core including an inner, high density, sphericalcenter core layer and an outer core layer disposed about said sphericalcenter core layer, wherein said spherical center core layer has aspecific gravity greater than 7.0 and a diameter of less than 0.380inches and comprises a blend including powdered metal and a first matrixmaterial comprising about 70 to about 30 weight percent polybutadieneand about 30 to about 70 weight percent polyisoprene, and said outercore layer comprises a second matrix material selected from the groupconsisting of thermosets, thermoplastics, and combinations thereof, andan inner cover layer formed about said dual core; and an outer coverlayer disposed on said inner cover layer.